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With graphs and tables 121-194 (Distributed July 28, 1918) 3 Morphology and Biology ot Some Turbellaria from the Mississippi Basin. By Ruth Higley. With 3 plates 195-288 (Distributed December 31, 1918) 4 North American Pseudophyllidean Cestodes from Fishes. By Arthur Reuben Cooper. With 13 plates 288-5^2 (Distributed May 31, 1919) ILLINOIS BIOLOGICAL MONOGRAPHS Vol. IV July, 1917 No. I Editorial Committee Stephen Alfred Forbes William Trelease Henry Baldwin Ward Published under the Auspices of the Graduate School by THE University of Illinois Copyright by the University of Illinois 1918 dlstribxtted march 6, 1918 LIFE HISTORY STUDIES ON MONTANA TREMATODES WITH 9 PLATES AND 1 TEXT FIGURE BY ERNEST CARROLL FAUST Contributions from the Zoological Laboratory of the University of Illinois under the direction of Henry B. Ward, No. 98 111 III liiilllMll|lM HH 738173 THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN ZOOLOGY IN THE GRADUATE SCHOOL OF THE UNIVERSITY OF ILLINOIS 1917 TABLE OF CONTENTS Pages Introduction 7 Methods of Investigation 7 Biology of the Bitter Root Valley 9 Morphology of Trematodes Foiind 13 Introduction 13 Embryology 14 Parthenitae (Sporocyst and Redia) 18 Cercaria General 23 Integument 27 Parenchyma 29 Musculature 30 Armature 31 Glands 32 Excretory System 36 Digestive System 43 Genital System 44 Nervous System 47 Description of the Trematodes Infecting Mollusks of the Bitter Root Valley 57 Introduction 57 Monostomata 58 Cercaria pellucida Faust 1917 58 Cercaria konadensis Faust 1917 61 olostomata 62 Cercaria flabelliformis Faust 1917 62 Tetracotyle pipientis nov. spec 64 Cercaria ptychocheilus Faust 1917 66 Distomata 68 Xiphidiocercariae 68 Cercaria crenata Faust 1917 68 Cercaria glandulosa Faust 1917 69 Cercaria diaphana Faust 1917 71 Cercaria dendritica Faust 1917 72 Cercaria micropharynx Faust 1917 74 Cercaria racemosa Faust 1917 75 Echinostome Cercariae 76 Cercaria trisolenata Faxist 1917 76 Cercaria biflexa Faust 1917 78 Furcocercariae 80 Cercaria gracillima Faust 1917 80 Cercaria tuberistoma Faust 1917 82 Pathology 84 Problems Presented 86 Interrelation of Trematodes 86 Relation of Trematodes to Other Groups 90 Life Cycle of the Digenetic Trematodes 92 Simamary 94 Species Described in this Paper 95 Bibliography .' 96 Explanation of Plates 1^2 71 LIFE HISTORY OP TREMATODES— FAUST INTRODUCTION During a two years' residence at Missoula, Montana, from 1914 to 1916 the writer became acquainted with the biology of the inter-mountain region of the Bitter Root valley. The heavy trematode infection of the animals in this locality has led to an investigation of the life history of the trematodes of the region. An opportunity is taken at this place to express appreciation to all who have aided in this study, but especially to Professor Henry B. Ward whose kindness and sincere interest have made the work possible. METHODS or INVESTIGATION This study is confined to the trematodes infecting moUusks. The majority of the collections were made by Mr. Norbert Sager of Missoula. A sketch map (text-fig. 1) indicates the location of each collection. The snails were shipped in damp green moss and arrived in excellent condition. These observations on living material gave data on the stages of develop- ment within the mollusk, on the methods of locomotion, on encystment, and on the excretory system. The worms were removed from the infected tissue and placed in a watch glass in 0.3 per cent saline solution. The change from the host tissue to the sahne medium usually caused rapid movement. It is essential that the excretory system be studied in the living material as, aside from the vesicle and the main trunks of this system, very little can be made out in the preserved material. The delicate structure of the flame cells and the finer capillaries makes it necessary that these organs be examined in living specimens, for in fixation they are likely to "collapse, even with the most careful technic. The organs of the digestive system come out equally well in living and preserved mounts. Some systems, as a rule, can be made out only from pre- served and stained material. The most important of these is the genital com- plex. For all ordinary purposes the material was fixed in Gilson's reagent, altho equally good results were obtained from a corrosive-acetic fixing agent. From the preserved material toto mounts and sections were made, using Dela- field's hematoxylin and EhrHch's acid hematoxyhn as stains. A strong counter-stain of eosin in the sections brought out remarkably well the nerve fibers of the worms. Wax models were made of the mature and immature stages of the nervous system of cercariae and parthenitae. Care was taken to keep the mounts acid-free, and for that purpose all reagents except the destaining fluid were made slightly alkaline with dessicated ILUNOIS BIOLOGICAL MONOGRAPHS [8 Text-figure 1. Sketch map of the Bitter Root Valley, Montana, showing localities where collections were made. 9] UFE HISTORY OF TREMATODES— FAUST 9 potassium acetate. Some specimens were fixed without any acid fraction in the reagent in order to preserve the excretory granules. These granules, as well as the mucoid cyst membrane of the encysted worm, gave beautiful biuret and xanthoproteic reactions, suggesting a tyrosine compound. BIOLOGY OF THE BITTER ROOT VALLEY The snails commonly found in the Bitter Root valley are Physa gyrina Say, Lymnaea proxima Lea., and Planorbis irivolvis Say. They have been identified by Mr. Bryant Walker of Detroit, Michigan. All of these snails were collected from the lower part of the valley, but Planorbis trivolvis was not found in the upper reaches of the river. These mollusks are the hosts of the trematodes considered in this paper. Two facts stand out predominantly in the study of these parasites: the large munber of species of trematodes in the snails in the limited range of the valley, and the high per cent of infection both among individuals of a species and within the individual of the species. There have been found in a single season's collection thirteen trematode species in the snails of the valley, and one larval trematode in the squaw-fish, Ptychocheilus oregonensis Richardson. A total of fifteen collections of snails was made during the fall of 1916 and four collections during May 1917. Seventeen of these collections contained trematode infection. Lymnaea proxima was taken eight times from five different localities, Physa gyrina was taken eleven times from eight different locaHties, and Planorbis trivolvis was taken three times from two localities (Table I, see next page). The infection record shows that the host is not specific. In the infection of mollusks with Cercaria pellucida the host around Buckhouse Bridge was Physa, while that up the valley was Lymnaea. Cercaria gracillima was found both in Physa and in Lymnaea in the region of Buckhouse Bridge from different collections. Cercaria trisolenata was found both in Physa and in Lymnaea in the region of Buckhouse Bridge and in the vicinity of Fort Missoula. While no parasite species was found in more than two of the three snails common in the valley, there is reason to beUeve that the third species of snail might be the host under proper conditions. This view is contrasted with that of Thomas (1883:106) who found that only one EngHsh moUusk, Lymnaea trunculata, "could serve as an intermediate host to the liver fluke," altho this writer suggested that other species of snails must serve in other countries as hosts to the worm. This preference for a particular moUusk in a particular locality, coupled with the abihty to select a different molluscan host in another locality, has been found to hold true not only for Fasciola hepatica, but also for Schistosoma haematobium (Leiper, 1916) and S. mansoni (Leiper, 1916; Lutz, 1916; Iturbe and Gonzalez, 1917). When two hosts so different structurally as Physa and Planorbis are equally heavily infected, it seems evident that the stimulus to which the miracidium of the fluke responds can 10 ILUNOIS BIOLOGICAL MONOGRAPHS [10 TABLE I DISTRIBUTION OF CERCARIAE IN THE BITTER ROOT VALLEY tn •^ 03 .2 .52 rt a .3 =^ t t "cS at 1 •c > O U > u O U o U o U V > o U V 3 ^ M M^ a & > se o o Si 4) il tn fa 0) 1 d o c73 5o ^ 3 .s 173 o o ^ ■^ tn 3 O fi c tn 55 a tn 3 O a I 1 73 ■1-1 3 O > a s s :^ ^^^ .6 ■u a o rt 1-1 O ti o 3 S in U fa U « « fa u . « "2 ttl o CQ o »-l cr o 0 rt 4J !U S •5.S '^ 5 >, •CO .2 « bO o 2'G 11 O 03 1 b^ M e 4 4 «-i •.-I gS3 pq ._ flO\ o\ ^ rtoo'-' |pL,<:o T3"0 CO\ (floo art !;?'C PL,3 U!-^ < Q l-H H «^ s < 1 C/3 eso c .STvO •c < <: 2 a to ^ S s| C/3 ^ ^ o ,,-i^,. « b i 1 05 £;> n- as CSQ pq M » 6<& 00 «^ .SiPg o II? 2 rt. 05 (S :^ ♦J "" Pi H O S J5§ t < =r f-4 C tf] III 10 so boo :il^- «o ill ^g CO ^ O— 1 ?5 w z » 03 ^ "^ w O w M 2: H Bx ij 3 ^ to o ?5 S w o ° W D o |5 23] UPE HISTORY OF TREMATODES— FAUST 23 the germinal epithelium of the parthenitae arose from a common type of germ cell. In other words, the germ cells of cercariae and parthenitae are homolo- gous. Stages in the phylogenetic development of the germinal epithelium may be outlined thus: 1. Germinal epithehum non-localized. Example, Cercaria diaphana (Fig. 79), C micropharynx (Fig. 94). Sporocyst cycle. 2. Germinal epithelium localized; no mouth or suctorial apparatus. Ex- ample, C. glandulosa (Fig. 67). Sporocyst cycle. 3. Germinal epithehmn localized; suctorial disc or attachment organ opposite germinal cell mass. Example, C. dendritica (Fig. 87), C. racemosa (Fig. 105). Sporcyst cycle. 4. Germinal epithehum localized opposite a true oral aperture, with phar- ynx and gut present. Example, C flabelliformis (Fig. 43). Redia cycle. 5. Germinal epithelium locaHzed and specialized into two sorts of con- jugating germ cells, male and female isogametes. (Theoretical.) 6. Male germ cells prohferated in numbers from the mass of germinal tissue at the posterior end of the body; female germ cells more highly differentiated. Example, C. gracillima (Fig. 149). Cercaria stage of hermaphroditic cycle. 7. Germinal cells massed into a small number of speciaHzed glands, called testes and ovaries. Example, C. pellucida (Fig. 18). Cercaria stage of hermaphroditic cycle. CERCARIA (general) The cercaria is the offspring of the parthenita. It is a highly specialized individual, homologous to the immature redia or the sporocyst. Its speciaU- zation has been accounted for by Ssinitzin (1910:38-56) because of 1) a con- siderable period of free-swimming hfe, during which it acquired a tail, and 2) a change to parasitism in the vertebrate, which was at first facultative, but later became obligatory. There are two types of modified characters to be accounted for in the cercaria, in addition to the original characters common to parthenita and cercaria. The tail, the well-developed muscle complex, the nerves innervating the muscle system, together with the sahvary glands and the sensory papillae — all of these bear evidence of a long period of indepen- dent life. When the organism became parasitic, first ectoparasitic, later endoparasitic, the highly developed muscular suckers with their nerve tracts were further developed, while the stylet organs and cystogenous glands were differentiated. The muscular specialization was of primary importance within the host, while the cyst served to protect the worm during the period of transfer from larval to definitive host. The cercaria varies in size, altho it is fairly constant for a particular family or genus. Holostome larvae reach a size of 0.63 mm. in length and 0.35 mm. in width (C. ptychocheilus). On the other hand some of the xiphidiocercariae are much more minute, 0. 18 mm. in length by 0.09 mm.in width.{C. micropharynx). 24 ILLINOIS BIOLOGICAL MONOGRAPHS [24 There are two types of movement in the cercaria aside from the apparent contraction and expansion of the body. One of these is concerned with the forward movement of the animal and depends on the cooperative action of the suctorial organs and the general bodily musculature. The other is caused by the flagellate action of the tail. The movement of the cercaria along a forward path reminds one of the rythmic action of a measuring worm. The oral sucker is always used as one organ of attachment, and the ventral or caudal suctorial disc supplies the other anchorage. With these two organs of attachment, the larval worm applies the oral disc to the object of contact, while it draws the posterior portion of the body forward by the contraction of all the longitudinal muscles. This places the posterior attachment advan- tageously near the oral disc, so that a relaxing of the longitudinal muscles and a synchronous contraction of the transverse muscles throws the cephalic portion of the worm far forward. In the forms with well developed muscula- ture, such as monostome and echinostome species, the larva may appear discoid on contraction, while the expanded worm wiU assume a length several times that of the normal body. All groups of cercariae possess an oral suctorial organ. For the second attachment organ there is a variety of accommodation. Undoubtedly the most advantageously formed organ of this second typo, is the one found in the Amphistomata, where there is a powerful suctorial disc at the posterior end of the body. Among the distomes there are many types of posterior suctorial organ, ranging from those with a prominent acetabulum not far from the caudal extremity, as in Stomylotrema pictum (Crep.) (Looss 1899:629), to those with a poorly developed acetabulum more cephalic in position. In the latter case there are frequently found auxiliary locomotor organs, such as those in the posterior pockets of the xiphidiocercariae. In some species there is only a suggestion of a paired suctorial organ, as in the larvae, Cercaria crenata (Fig. 55), and C diaphana (Fig. 76). In others there is the additional spinose complement (C. glandulosa, C. dendritica, and C. micropharynx). These spines are of important fimction on rough surfaces where the disc can take hold with difficulty. Altho there is considerable difference in the rapidity of movement of the various species studied, C. glandulosa was by far the most rapid in movement of all the cercariae observed. The spinous outgrowth of the acetabulum is of advantage in locomotion, catching hold where the un- armed sucker can not operate (C glandulosa, Fig. 60 ; and C. gracillima, Fig. 142). Muscular development in the holostome larva is confined entirely to the suctorial apparatus, since there is no distinct tail portion. This type of sucker is derived from the distome type. With the translocation of the genital opening to the posterior end of the body, the primitive genital pore has come to be used as an accessory suctorial organ (Cercaria ptychocheilus, Fig. 47). The most unique modification is found in the tetracotyle type. Here there have arisen two lateral accessory suctorial grooves (Fig. 41), and lappet modifications of 251 LIFE HISTORY OF TREMATODES— FAUST 25 the acetabulum. All of these come to be enclosed in a common pocket which acts as a large sucking cup (Fig. 40). There is practically no locomotion in these species, since movement is confined almost exclusively to the sucking reflex. In the monostome no acetabulum is present, yet the cercaria performs the processes of locomotion par excellence. The pair of posterior locomotor organs replaces the acetabulum in the measuring worm movement. In Cer- caria pellucida and C. konadensis, as well as in C. urbanensis Cort, these organs consist of posterior inpocketings of the integument. In C. imbricata, Looss (1896, Fig. 151) there is an internal pocket. In C ephemera Nitzsch (Ssinitzin, 1905, Fig. 75, 76) there are hook-shaped spines. Cort (1915:15) finds that they " apparently have no suctorial function, since no muscles are present and the central cavity contracts while the projection is extended." A careful study of living and preserved specimens of C. pellucida, C. konadensis, and C. urbanensis shows that these three American species have no spinose or other integumentary modifications. However, their function is found to be distinctly suctorial, and not "analogous to setae," as Cort believes. Typical drawings for the locomotor organs of any of these three species are shown (Figs. 16, 17). As will be seen in figure 16, there are four muscles which are attached to the pockets. By a contraction of the pair xx the pocket disc is applied to the surface of the contact body; by a relaxation of xx and a con- traction of yy the pocket is released and pulled forward by the general bodily contraction. This has been observed repeatedly in so convincing a manner that it leaves no doubt as to the structure or function of the organ. In addition, in C. konadensis (Fig. 21) a group of glands just anterior to the locomotor pockets pour out a mucous secretion at the time when the disc is applied to the contact organ. The locomotor pockets perform a similar function and in a similar manner to that of the secondary suctorial disc or acetabulum of amphistome or distome, altho these organs are in no sense homologous. The significance of the spines in connection with the caudal locomotor pockets of distomes has been regarded by Leuckart (1886:128) as deserving special consideration. In Cercaria armata he considers them as serviceable in keeping the tail attached to the body after the constriction between the two parts has become deep. Looking into the phylogenetic significance of the spines of the same cercaria species, Ssinitzin (1911:68) regards them as indicating a bifid ancestral appendage of a caudal nature. In view of the fact that these pockets actually function similarly to the locomotor pockets of the monostomes, and are more than likely the ancestors of the monostome type of pocket (Fig. 12), it seems hardly worth while to find a more obscure meaning in the structures. The tail is the portion of the cercaria showing preeminently the adaptation of the organism to free-swimming life. In such forms as C. setifera (Monticelli, 1914), C. pennata and C. plumosa (Ssinitzin, 1911, Figs. 76-79), the prolonged free-swimming existence has given rise to setae, spines and scutes. 26 ILLINOIS BIOLOGICAL MONOGRAPHS [26 The tail arises as a median posterior protuberance, bilaterally symmetrical, and is, according to the views of Ssinitzin, phylogenetically a paired organ. This thesis is supported, in part at least, by the fact that the excretory trunks arise as paired organs in both the body and the tail. In the furcocercariae the caudal tubules remain separate in the rami of the tail and also in the "eyelet anastomosis" at the junction of the body and the tail. There devel- ops in the tail the usual complement of muscles, a transverse layer externally and a longitudinal group more median. Within the cylinder of muscles is the group of parenchyma cells surrounding the excretory tubule. In the tails of distome cercariae (Figs. 99, 133) the excretory vessel is a paired structure, separated in the middle by a parenchymatous partition with one or two nuclei in each section of 7 /z thickness. Some schistosomatid larvae have, in addition, eleven or twelve pairs of oblong cells just lateral to the excretory vessel. The tail of the monostome is characterized by extra large longitudinal muscles with prominent nuclei. The portion within the longi- tudinal muscle cyHnder differs in structure in individual species. In C. pellu- cida there is one ring of very large parenchyma cells situated around' the excretory vessel. There are eight to ten cells to each transverse plane of 7/i. In C. konadensis and C. urhanensis there are glandular cells within the paren- chyma ring; they are large and crowded with granules. In both of these species (Figs. 25, 32) these cells are arranged in six paired groups. In C. konadensis there are many cells to each member of the group, arranged in pyramidal fashion with the apex directed distally. Thus the largest cells in each group (Fig. 27) are proximal. These cells He next to the excretory vessel. Cort has described the cells of C. urhanensis thus: "extending the length of the tail and forming a core are two rows of long cells which are close together and have their long axes parallel with the length of the tail. . . , They are full of heavy staining granules. . . There is nothing suggestive of the possible function of these cells. " He has failed to observe the exact number of these cells (six pairs) and is in error in considering them as a core extending the whole length of the tail, for they alternate with non-glandular tissue in about half of the extent of the organ. Their structure is probably glandular. In C. urhanensis these cells arise from undififerentiated parenchyma cells (Fig. 2>2>). They soon appear as falciform cells in trans-section (Fig. 34), separated in a median sagittal plane by a partition arising between two intermediate parenchyma cells, which soon differentiate into a muscular lamina. The lamina arises before the excretory tubules differentiate as distinct lumina among the parenchyma cells. Thus the bilateral symmetry along the median sagittal plane is well show^n. The excretory vessel is single in the mature C. pellucida and C. konadensis, but remains paired in C. urhanensis. Looss (1893:24-28) cites the epithelial cells of the tail of cercariae as good examples of " Blasenzellen, " where all cell elements of the mesenchyme usually become " Blasenzellen ", and where no true glands take their place. The study of C. konadensis, C. urhanensis, and C. gracillima, shows that axial cell glands are present, and that they are derived from the parenchyma, Moreover 27] LIFE HISTORY OF TREMATODES— FAUST 27 where these special gland cells are not present, as in C. pellucida, the parenchyma cells are more vesicular than where they are present. The writer is in accord with Looss's view that there are no indifferent cells remaining in the tail. Hence the tail, when separated from the body, can not meta- morphose into a sporocyst or redia, as the older writers believed (Pagenstecher, 1857:15). INTEGUMENT The covering of trematodes and cestodes has been the subject of con- siderable controversy. Four main theories have been proposed. The Bloch- mann theory (1896) assumes that the cuticula of trematodes and cestodes is a true morphological cuticula secreted by the hypodermis, as in other inver- tebrates. A second theory, presented by Brandes (1892), postulates that trematodes have no subcuticula in the true sense of the term, and what has been considered as such is nothing more than the true parenchymatous con- nective tissue. Nevertheless, the body covering is a true cuticula, secreted by special glandular cells of epidermal origin just beneath the cuticula. The presence of apparent nuclei in the cuticula has revived the old idea of Wagener that the cuticula is a metamorphosed epithelium. Goto has subscribed to this theory in his study of ectoparasitic trematodes (1894:6-13), defining three layers, an outer cuticula, a subcuticula, and a basement membrane. This is also the interpretation Monticelli has put on the body investment of Cotylogaster michaelis (1892:189), which he claims to possess an "ectoderma sinciziale di aspetto cuticuloide. " More recently Gary (1909:646) has ad- vocated this view. Pratt (1909:721) is incHned toward Leuckart's theory that the cuticula is of parenchymatous origin, a derivative of the peripheral portion of the parenchyma. The species of larval trematodes studied by the writer are uniform in showing that the epidermal layer, developing into a syncytium in many cases, is present in the early stages of the sporocyst, redia, and cercaria. In the parthenitae, especially in the redia, this layer may persist until the germ balls within are ripe and ready to escape. In the cercaria the epidermal tissue is present in early life as a syncytial layer investing the larva. In the mature cercaria it is sloughed off. The "cuticula," when present, arises from below the epidermis. It is a discrete layer underneath the epidermis, or it impregnates the epidermis from below. In the latter case the nuclei are always superficial, usually rising above the surface as small tuberosities. In the monostome group, the redia possesses a syncytium of ectodermal cells impregnated here and there with granules of a secretory nature. The cercaria develops a well-defined epidermis which later (Fig. 37) becomes syncytial and is sloughed off. Underneath this the "cuticula" is distinctly cut off from the epidermis on the outside and from the mesodermal tissue beneath. Among the latter are the special parenchyma cells with aciculate pseudopodia, corresponding to Blochmann's "Epithelzellen" (1896:7). These differentiated parenchyma cells have no connection with the "cuticula" in 28 ILLINOIS BIOLOGICAL MONOGRAPHS [28 the developing or mature cercaria of this group. A non-nucleated epidermis is shown in the process of sloughing off for the hemistome cercaria (C ptychocheiliis, Fig. 54) . Underneath is a distinct layer of ' ' cuticula. ' ' B eneath the "cuticula " is a lining of transverse and longitudinal muscle fibers. Median to the complexes of the longitudinal muscles are the complexes of the con- nective tissue. The whole structure, from the inner wall of the "cuticula" thru to the free parenchyma, is infiltrated and bound together into a single mass by a mucoid secretion. This secretion is indifferent to stains. The epi- theHal cells of the complex send out long processes toward the integument, so that the processes penetrate into the latter. These cells suggest gland cells, concerned with the secretion of the "cuticula." They are not potentially different from the underl>'ing parenchyma. Among the distome larvae the writer has studied the "cuticula" problem for echinostomes, schistosomes, and xiphidiocercariae. The redia of C. trisole- nata possesses an ectodermal reticulum in which are foimd large vesicular nuclei. This covering is impregnated with large granules which are indifferent to stains. In the cercaria of this form (Figs. 128-133), there is an ectodermal layer present, very thin, with the nuclei arising from the surface as minute tuberosities. Beneath this is the thick layer of "cuticula." The epidermis has been lost in the tail. No "Epithekellen" are visible in the mesenchyme complex. For the schistosome larva, C. gracillima, there are definite nuclei present as minute papillations rising above the surface of the epidermal layer. The sporocyst of this form has no "cuticula." The body wall consists of a single layer of ectoderm cells, arranged end to end, the nuclei of which are oval to subspherical. In the distome, C. glanduLosa, the sporocyst wall is composed of a single layer of epidermal cells, with falciform nuclei. In the cercaria the epidermis is present only in individuals where the taU is still attached. Here nuclei are present in the peripheral layer of the body, but are not foimd in the covering of the tail. The "cuticula" is a thin envelope around the circular layer of muscles. The study of these trematodes with reference to the problem of the integu- ment has led the writer to set aside the view that the "cuticula" is ectodermal in origin, because the ectoderm is superficial, lying outside the "cuticula." The impregnation of this layer with cuticular granules might lead one to be- lieve that the two layers are one, but the earlier history of the layers shows that this conception is erroneous. No hypodermis is f oimd in any of the species studied. Consequently the Blochmann theory can not hold for these species. No special gland cells have been foimd to support in its entirety the theor}' of Brandes. On the other hand the evidence of this study points to the sus- taining of Leuckart's theory of the parenchymatous origin of the basement membrane on the following grounds. 1) In all the species the basement mem- brane arises from tissue beneath the ectodermal layer. 2) In all cases where there is an ectodermal layer only (in sporocysts), no basement membrane is found. 3) The heaviest layer is foimd in species where the parenchj-ma has a widely diversified potency, such as salivary, cystogenous, locomotor and 291 LIFE HISTOR Y OF TREMA TODES—FA UST 29 mucin glands, 4) The "Epithelzellen" of the monostomes and holostomes (Figs. 37, 54) are characterized by large vesicular nuclei and vacuolated cyto- plasm, similar to the "Blasenzellen" of Schwarze (1886) and Looss (1893). They are modified parenchyma cells differing from the underlying layers not in potency but in location. 5) As the secretory cells for the basement mem- brane, these parenchyma cells have developed long acicular pseudopodia toward the membrane and, in the larval holostomes, have penetrated into it. All of these data point toward the parenchymatous origin of the basement membrane. PARENCHYMA Soon after the fundaments of the digestive and nervous systems of the cercaria are laid down, certain cells of mesodermal origin of the germ ball become ovoid and are filled with milky white granules. These are cystogenous cells, the "Stabenkornchen" of the German writers and the "cellules a bS,tonnets" of the French. They develop most conmionly in monostomes, amphistomes, and such distomes as form a heavy cyst. Other portions of the mesoderm are differentiated as the germinal epithe- lium and the muscle layers. The remainder of the mesodermal cells is for a considerable time potentially great, and remains undifferentiated (Looss, 1893:29). They constitute the parenchyma. Looss has compared these cells of the mesoderm to the cambium of the plant. They are the "nicht- veranderten Zellen," on the multiplication of which depends the growth of the minute larva to the relatively large adult. As the animal grows the cells of this region become more vesicular, vacuoles appear within the cytoplasm, and acidophilous granules appear within the cell. The intercellular spaces become more and more prominent. The cells are held together by bands of ragged connective tissue which, for the most part, is the outgrowth of the interstitial cells. Within this parenchyma complex there appear large tubular lumina in certain definite regions, and, leading into these, tubes and smaller tubules. These are the excretory tubes; at the ultimate ends of these are found the capillaries and the flame cells (Looss, 1892:162; Thomas, 1883:116- 118). In the schistosome cercariae studied the main group of cilia is not at the extreme ends of the ducts, but in a pocket in the posterolateral part of the main trunks (Figs. 143, 145). It is of importance to emphasize here that these excretory trunks and tubes are not lined by a wall of specialized cells, but are merely lumina among certain cells of the parenchyma. It seems highly probable that Looss 's view is correct as regards the flame or "Trichter, " that it, too, is an intercellular lumen, into which the parenchyma-cell cilia protrude, and that it is not in a hoUowed-out cell. The cilia are definitely outgrowths of the single cell at the head of the capillary (Fig. 138), a cell which is differentiated from the sister cells of the parenchyma by the possession of a much smaller nucleus and densely granular protoplasm. 30 ILUNOIS BIOLOGICAL MONOGRAPHS [30 MUSCULATURE The muscle systems of the parthenitae and the cercariae are confined, for the most part, to the peripheral and splanchnic regions. The peripheral muscles consist of an outer series of radial muscle fibers and an inner series of longitudinal fibers. A third series, the dorsoventral, which is common in the adult forms, is suggested at times in the body of the cercaria. The muscles of the intestinal tract consist of a longitudinal and a circular series. The peripheral system Ues directly beneath the basement membrane. It opens interstitially to permit the growth of the processes of the parenchyma cells which secrete the basement membrane. The outermost layer is the cir- cular series. It may consist of a single band one cell in thickness or it may in- clude a cylindrical band several layers thick (Figs. 37, 54, 97, 128). Within this is the longitudinal series. Usually here the individual fibers of the bundles are separated from one another by a considerable interval. The fibers are longer and fewer than those of the circular series. A section of an adult trema- tode shows, in addition to these, an obUque series of fibers. These obHque fibers give the appearance in section of a diamond pattern. In another type, the dorsoventral, the fibers run at right angles to the frontal plane. In the holo- stome cercaria (Fig. 54) no such series is found, altho the longitudinal series is so arranged that the fibers are on edge and might be taken for the dorso- ventral series. The view of Bettendorf (1897:315,316) that the "Epithelzellen" of Blochmann are really longitudinal muscles, can not be considered vaUd, since in the same sections the former are indifferent to stains and the latter are deeply stained by the same methods of technic. In the oral and acetabular suckers and frequently in the phar>-nx there exist the transverse, longitudinal and obUque series of muscle fibers, inter- woven into an inseparable complex. These are best developed in the Am- phistomata. Since the redia which produces germ balls is an adult and the cer- caria is an inunature individual, it is not surprising that the pharynx of the redia is fibrous, with few nuclei and large vacuoles, while the pharjiix and suckers of the cercaria are composed of cells practically undifferentiated. In the rediae the fibers can be traced to the myoblasts. The main deep-seated system of muscles for the cercaria consists of the muscle band series of the digestive tract. In the holostome (Fig. 54) an additional muscular activity has been assxmied by the cirrus pouch. Aside from these no muscle striae are developed in connection with the genitalia in the larva. The ceca of the digestive tract are covered with an outer and an inner series. The former are longitudinal fibers and the latter are circular fibers. This is in conformity with the muscular layer studies made on other Platyhelminthes. Histology of the muscle cells. When Bettendorf (1897) showed the connection between the muscle fibers and the myoblasts an important step was made in the knowledge of the intimate structure of the trematode muscle cell. The present study corroborates Bettendorf 's work. The nuclei of 31] LIFE HISTORY OF TREMATODES— FAUST 31 the myoblasts are oval (Figs. 118, 119). The cells very early send out long protoplasmic strands along well defined paths. While the processes from the myoblasts may emerge from any part of the cell, the longitudinal strands are always directed in a longitudinal plane, and the circular fibers are always circular. A unique picture is presented at the point where the furcae of the digestive tract arise (Fig. 118). Here there are two anterior processes running cephalad, and three strands proceeding caudad along each cecum. The chromatin in the nucleus of the myoblast is usually confined to the karyosome. ^ ARMATURE OF THE TREMATODE The miracidiimi and sporocysts are not ordinarily provided with hooks or any piercing armature. The redia is usually conspicuous because of its oral sucker, pharynx and gut, and not because of any armature. In the cercaria, however, are found, even in some of the most delicate species, spines covering the basement membrane, especially in the region of the head. In the special group of the stylet cercariae the stylet is the larval organ which is of specific systematic value. It is not a universal rule, however, that all rediae and sporocysts are un- armed. At times a modification of the posterior wall of the redia is produced as in the redia of C. biflexa, where the terminal organ is spinose (Fig. 141). Leiper and Atkinson (1915:202) found the second sporocyst generation of Schistosoma japonicum to be covered with a spinous integument. More conspicuous is the prepharynx organ of the redia of Cercaria pellucida (Fig. 7). This organ is four-lobed, and has on the outer side of each lobe long spines projecting forward and small spines directed laterad. The use of such a weapon within the soft parts of the host tissue produces untold injury. No armature has been observed on the body of any monostome cercaria. The holostome, Tetracotyle pipientis (Fig. 47), has a spinose covering over the entire body and special spines in the region of the acetabulum and accessory suctorial grooves. Spinose modifications are common in the distome group, and in some cercariae, setiferous modifications of the tail. The types which the writer has examined have the armature confined to the body. They will be discussed under the headings of 1) general body spines, 2) spines of the oral aperture, 3) collar spines of the echinostomes, and 4) the stylet organ of the xiphidiocercariae. In addition there are the spines at the posterior end of the trunk in the caudal pockets. Their probable locomotor function has made it necessary to consider them in another place. In many cercariae there is a tendency for the entire bodily integiunent to become modified so that the surface bristles with needle-like spines. These are usually arranged in a regular diamond pattern, and are more fully devel- . oped at the anterior end of the body than in the caudal portion (Figure 90). This condition is found in some xiphidiocercariae and some echinostomes. The spines are always pointed forward. They are more fully developed in the anterior region of the body. 32 ILLINOIS BIOLOGICAL MONOGRAPHS [32 Of a somewhat more limited distribution is the oral armature of spines in the schistosomatid C. gracillima (Fig. 142) . These spines are turned into the body with the inpocketing of the oral sucker-pouch, so that the animal in the condition of contraction appears perfectly aspinose except for the armature of the acetabulum. But with its protrusion the oral sucker is crowned with a sohd cap of spines. The hood of spines of the echinostome group is specialized and valuable in systematic work. It is usually an incomplete ring, consisting of a circlet of spines around the dorsal side, extending ventrad into the middle half of the body. Dietz (1910) has sketched 63 figures of spine characters and numbers in his monograph on the Echinostomidae of birds. The adult echi- nostomes of North America have received little attention and in consequence of the difficulty in working out the exact spine number in the larva a descrip- tion of the specific spine characters of the cercariae will not be worth while until more attention is given to the adults of the family. The stylet is the unique larval organ in the group of the xiphidiocercariae. It might be more properly called a quill than a stylet, for its value as an organ of piercing is questionable on account of its frailty and frequently disadvanta- geous leverage. It is a mucoid structure, situated in the dorsal wall of the oral pocket, well supplied with muscles to work it in any direction anteriad and laterad. It is fully formed only in the mature cercaria, and is carried into the cyst (Figs. 84, 85). Quite generally the stylet is recognized as of specific systematic value, and is therefore figured in systematic descriptions (Liihe, 1909:189-200), but the stylets as they are figured are so generalized as to be of little value in the identification of species. The stylet is of specific value, but this value lies in the details of the organ rather than in the general out- line. (See Figs. 57, 61, 77, 83, 91, 102). The stylet is usually a weak organ mechanically and poorly levered. However, it is resistent to chemicals and indifferent to dyes. The stylet of Cercaria glandulosa is extremely delicate, so that it goes to pieces immediately when a cover glass is pressed down on a water-mount of the worm. The stylet, as a rule, is hard to observe in preserved mounts. GLANDS OF THE LARVAL TREMATODE Glandular organs in the trematode may be distinguished as dermal, salivary, mucin, cystogenous, genital, and locomotor. The dermal glands are those imbedded in the subdermal tissues, are unicellular, usually flask-shaped, and have a small duct opening to the exterior. The saUvary glands include all of the unicellular glands which open into the digestive tube. Mucin glands are paired, right and left groups of one to several gland cells emptying into the oral pocket thru long attenuate ducts. Since mucin is a constituent of salivary glands, these glands are modified salivary glands. Cystogenous glands are imbedded in the parenchyma and are usually filled with rhabditiform granules which superficially resemble the dermal rhabdites of the Turbellaria but are 33] LIFE HISTORY OF TREMATODES— FAUST 33 not to be confused with them. The cystogenous glands function in the for- mation of the larval cyst at the time when the transfer to the secondary or definitive host is to be made. Genital glands, in the sense employed here, include only the auxiUary gland elements of the genital system and do not refer to the sex glands themselves. Locomotor glands arise in connection with the locomotor organs in the posterior part of the body. The dermal glands are of adult significance. Looss (1894:125) has found them in all groups of adult trematodes studied, but he does not later (1896: 219, Fig. 176, glcu) record them for any cercariae except C. vivax Sons. No dermal glands have been found by the writer in the course of the present study. Salivary glands are probably present in all groups of cercariae and in some rediae. In the simplest form they are nothing more than pyriform cells in the region of the digestive tube. Thus the monostome cercaria, C. imbricata, described by Looss (1896:195) as having a pharynx without a bulb, has unicell- ular glands massed around the tube in the pharynx region. The f urcocercariae, with no true pharynx, have a similar group of cells in the pharynx region, so closely massed together as to lead Looss to considering them a true phar)mx (1896:220, Fig. 176, ph). In structure these masses of glands in the f urco- cercariae look superficially like a pharynx (Fig. 142), but on cross- section the cells of the complex are found to be unmistakably glandular (Fig. 152). A modification of the type of sahvary gland just described has been ob- served in Cercaria micropharynx, C. diaphana, and C. glandtdosa. In these species the cercariae show not only the muscular pharynx, but also a large group of gland cells around the digestive tract. In C micropharynx (Fig. 93) the glands are prepharyngeal, grouped in a spherical mass around the oral chamber. They are minute cells, about 3/x in trans-section. The glands of C diaphana (Fig. 76) exhibit a maximum glandular growth in the vicinity of the pharynx proper. Several hundred gland cells about 3/i in diameter surround the pharynx. A case of secretion along the entire digestive tract is found in C. glandulosa (Fig. 60). In this species the glands are much larger than in the two preceding species, about 6/i in cross section and 12/i to 25)u in length. They are formed along the entire course of the lumen, from the ori- fice to the blind end of the ceca, altho they are best developed in the region of the pharynx. A distinctly different type of gland is that termed the "stylet gland." It is so-named because of its frequent occurrence coincidently with the stylet organ of the xiphidiocercariae. But since it occmrs, too, in furcocercariae and in echinostome cercariae, where there is no trace of a stylet, the evidence supports the view that this type of gland is more generalized and more primi- tive than the stylet organ. These glands are found in the cercariae of the distome groups examined by the writer, and in the redia of the holostome, C. flabelliformis. They are bilaterally symmetrical, lying outside the intestinal furcae, behind the region 34 ILLINOIS BIOLOGICAL MONOGRAPHS [U of the pharynx. They open thru long-necked ducts into the oral pocket. The glands are in masses; they vary in the number of cells from four in each lateral mass of some furcocercariae (Fig. 144), to eight or ten in the stylet cercariae, while in the echinostomes they run as high as 1 10 on each side of the esophagus (Fig. 134). In general the cells are characterized by a densely staining gran- ular protoplasm and a highly refractive nucleus, which remains hyaline when treated with hematoxyhn dyes. Most interesting is the type presented in Cercaria crenata (Fig. 55), where there is a differentiation of inner and outer groups of the glands on each side of the gut. These groups have individual canals to their exit at the oral pocket. The outer series consists of six glands, comparatively small, Sfx to 9/i in diameter, goblet-shaped, extending caudad to the midacetabular region. They are finely granular and are best studied in living mounts. The inner series consists of five cells, two of which are situated just behind the pharynx and the other three postacetabular, thus causing the inner series to be divided into an anterior and a posterior group. These inner gland cells are llju to 15ju in diameter, and coarsely granular. Their difference in structure suggests a functional difference. The mucin glands of the redia of C. flabelliformis are paired structures, lateral and dorsal to the digestive pouch, consisting of a single series of six cells which open thru a common tube into the pharynx region of the redia. The cells are similar in structure to the mucin cells of the cercariae of other groups, altho no such glands have been recorded from the cercariae of the holostome group. Only one other case has been reported for the redia, that for the parthenita of Cercaria equitator by Ssinitzin (1911:52, Fig. 50). In this redia the gland cells consist of a single cell with a wide duct to the pharynx region. A similar pair of unicellular salivary glands is figured by Looss for the miracidium of Schistosoma haematobium (1896, Fig. 113, glcph) and by Miyairi and Suzuki for the miracidium of S. japonicum (1914, Taf, 2, Figs. 1, 2). This occurrence of the mucin glands in the miracidium, redia, and cercaria of various groups, and the fact that they pass into the intermediate host along with the larva (La Rue, 1917), show that these organs are of fundamental importance in the economy of the worm. That these glands are of more specific character than the ordinary salivary and epidermal cells of the trematodes is demonstrated by their differential staining reaction. The usual hematoxylin dyes show a great nimiber of granular protein inclusions. Recently La Rue (1917) has shown that these glands in Cercaria marcianae have "mucus" in their ducts, because of, the staining reaction with toluidin blue and thionin. However, since the glycopro- tein of salivary digestion is mucin (Mathews, 1915:323), it is more exact to designate these structures as mucin glands. A t3^e of gland undoubtedly common to all cercariae is the cystogenous gland. It is a unicellular organ in the parenchyma just beneath the integument. In some groups this cell may be small and in the midst of parenchyma cells (C glandulosa, Fig. 62). In other groups the cystogenous cell is very large and conspicuous as in the species C pellucid a (Fig. 14), C dendritica 35] LIFE HISTOR Y OF TREMA TODES—FA UST 35 (Fig. 85), and C. trisolenata (Fig. 132). The material within the cyst cell is usually milky, semi-opaque, either homogeneous or granular. In most cases the contents consist mainly of the rhabditiform granules, which are indif- ferent to dyes. These granules are not attacked by weak acids or alkalies, but are digested by strong acids or bases. It seems probable that they are of a derived protein nature. The formation of the cyst varies in the types studied. In the majority of the species the cyst is a firm envelope with a free space around the embryo, more or less filled with a watery fluid (Figs. 41, 84, 118). On the other hand, some of the cysts are more mucoid in structure, with a granular viscous inner portion and an outer jell (Fig. 11), The method of encystment differs in different species. In the monostome where the encystment is rapid and an entire lot of mature cercariae encysts in two or three minutes after they are freed from the redia, the process is so rapid that the tail is not entirely cut off until the major portion of the cyst as formed (Figs. 9-11). Where the time of encystment is considerably longer, OS in C. trisolenata and C. dendritica, the tail is discarded long before the process of encystment actually begins. Encystment is an adaptation on the part of the larva to the change in environment. In two cases studied it takes place within the liver of the primary host (C. micropharynx and C. biflexa). It is highly probable that in these forms encystment was the result of temperature stimuli, since the worms were secured in November when the winter had already set in. It is apparently an adaptation for "wintering over." In only one group, the furcocercariae, has there been no record of encyst- ment of the cercaria. Here the tail is dropped only under the pressure of the cover slip or when the worm begins to disintegrate. La Valette (1855:34) expresses this condition for his forms when he writes of the larvae: "Cercariae cystibus non indutae in animalium vertebratorum intestinis pereunt." The phenomenon of encystment is one which has been observed by many investigators. It has been seen and described very accurately by La Valette, Moulinie (1856), Pagenstecher (1857), and a long line of later investigators. Moulinie refers to the studies of earlier workers on encystment, mentioning von Siebold (1835) and Steenstrup (1842). But the credit for the first record of encystment undoubtedly belongs to Nitzsch (1807). Later (1816) this writer records his observations on the encystment of Cercaria ephemera. The review of Nitzsch in Isis describes the process of decaudation and en- cystment as observed by Nitzsch, and shows that this worker expected the cyst to develop the following year. Fantham 's criticism of Nitzsch is essen- tially unjust (1916:12), since Nitzsch considered the cyst to be dormant ands set dead. The process of encystment has been described in detail by Thomas in his work on Fasciola hepatica (1883:129). Encystment here conforms to the rapid type described for the monostome C. pellucida. "The tail is sometimes shaken off before encystment begins, but, as a rule, the tail remains in con- nection with the body during the process, and continues to be energetically 36 ILLINOIS BIOLOGICAL MONOGRAPHS [36 lashed from side to side, until finally a more vigorous movement detaches it. The whole process is very rapid, and in a few minutes a layer of consid- erable thickness is formed, whilst its substance begins to harden. " EXCRETORY SYSTEM The excretory system is the most dehcate of the four important systems o the trematode. It can be worked out with precision in the Uving animal, but in preserved material it is impossible to find more than the main trunks of the system. In all of the cercariae and parthenitae described in this paper the excretory systems have been studied from living material. Altho there are many individual differences within groups, yet the fundamental uniformity of groups is evident. A. The Monostomata. The main features of the excreton,-^ system of the Monostomata are the two main trunks arising from a common point just behind the median eye-spot or median pigment center, and proceeding posteriad and laterad to the posterior part of the body, where they join one another in the common vesicle. The bladder opens to the outside thru the excretory pore, which is not terminal but slightly dorsal. The main excretory trunks are filled with large refractor}' granules, more extensively described on p. 42. The continuous circuit of the system provides for the transfer of granules and other waste products from right to left and reversely, dependent on the contraction and expansion of the several parts of the animal. The bladders of the various species differ considerably in size and structure, but as a whole they may be placed in two sub-groups. In the trioculate forms, such as Cercarin pdlucida, in dorsal view the bladder is distinctly trilateral when relaxed, with the excretory pore at the posterior horn. This same type is found in C. ephemera Nitzsch (Ssinitzin, 1905, Fig. 76), and in C. imbricata Looss (18%, Fig. 148), and also in C. zostera (Ssinitzin 1911, PI. 1, Figs. 14, 15). In action, however, due to the muscular movements of the posterior portion of the body, the anterior portion of the bladder may seem to be a separate organ opening into the bulbous posterior portion of the vesicle thru a con- stricted area. In the binoculate tj'pes, on the other hand, the bladder is spheri- cal, with the excretory trunks emptying into the extreme lateral reaches of the vesicle. The excretory pore in these species is subterminal rather than termi- nal. The only binoculate species known are C. lophocerca (de FiUppi, 1857, PI. 1, Fig. 3), C. itrbanensis (Cort, 1915, Fig. 5), and C. konadensis. Lebour (1907:443, PL X, Fig. B) describes the bladder of C. lophocerca as semilunar, but from her figure it appears more reniform than lunar. Cort does not describe the shape of the bladder of C. urbanensis, or state its size. The writer has found it to measure 50/i to 60/i in median sagittal line and 60ju in transverse section for preserved material. The excretor)'^ pore of this species is large, some 20^1 in diameter; it is weakly muscular (Fig. 35). In C. konadensis (Fig. 29) the bladder is smaU, 14)ii to IS/x in diameter. The excretor)' pore is cor- respondingly small, 3n to 4^i in diameter, and weakly muscular. 37] LIFE HISTOR Y OF TREMA TODES—FA UST 37 The excretory system in the tail of monostomes is simple. It consists of a median tubule, with tributary laterals, which swell in the proximal region and empty into the common bladder of the trunk. B. Holostomata. The excretory systems of Holostomidae and Hemi- stomidae are sufficiently different to require separate treatment. 1. Holostome type. No accurate or detailed description of the tetracotyle type of excretory system exists. De Filippi (1857, Fig. 26) has pictured two laterals for C. vesiculosa, arising from nimoierous tubules in the anterior part of the body. The connection of these tubes in the region of the bladder is not clear. Altho his sketch was made ''to show particularly the lateral vessels," it gives no adequate conception of the fundamental vessels of the system. Brandes (1891:569) merely states that the "system reaches into all parts of the cone; an especially large canal passes longitudinally thru the anterior wall of the cone. " Only a faint suggestion of the system is figured by Rosseter (1909, Fig. 17), for Holostomum excisum (von Linstow). Brown (1899, Fig, 11) has worked out an interesting but unusual type. In view of the lack of definite data concerning the excretory vessels of the holostomid group, it seems advisable to describe the system for the species Cercaria flabelliformis. The excretory system of Cercaria flabelliformis is shown in figure 39. At the extreme posterior end of the worm, situated slightly dorsally, is the excretory pore. It is the opening of a relatively small bladder no larger than the pore itself. At its antero-lateral horns two large trunks arise, considerably inflated in their posterior portion. They may be traced forw^ard along the inner reaches of the digestive ceca until they reach a place about two-fifths the dis- tance from the anterior end of the larva. Here a transverse canal is found, with a median connection between the two trunks, and lateral transverse tubules. The lateral tubules drain the part of the larva posterior and lateral to them. Between them and the main longitudinal trunks are found a great number of anastomoses. Anterior to the median transverse canal the tubules spread out in fan-like arrangement, running to the sides and front of the worm. Apparently this system was originally distome in character, but was made over to suit the needs of a modified distome larva. The longitudinals are clearly those of the Y-type so common to the excretory system of the distomes. On the other hand, the transverse tubes and the anastomoses of the postero- lateral reaches are new structures. The entire system is filled with minute refractory granules which facilitate the tracing of the courses of the various vessels. 2. Hemistome type. This type has been worked out in faithful detail both in the larva (Diplostomulum) and in the adult. Hence a discussion of the excretory system of C. ptychocheilus will be limited to the points of diver- gence from the previously described species. The earliest larvae of this group to be accurately figured are Diplostomulum clavatum (Nordmann) and D. volvens (Nordmann) (1832, Taf. II-IV). From the elongated bladder there arises a bicornuate structure which proceeds forward and outward for a short distance. A bifurcation of each cornu then 38 ILLINOIS BIOLOGICAL MONOGRAPHS [33 takes place, so that there are two pairs of vessels to proceed forward, an inner and an outer pair. They run forward to a plane in front of the middle of the body, where they unite and run cephalad as a single vessel. A transverse vessel is found posterior to this union; this vessel connects the two sides of the system. Brandes' diagram for the excretory system of D. abbreviaium (1891, Taf. 39, Fig. 17) differs from this type only in the details and not in the main features. The system of Cercaria ptychocheilus (Fig. 49) has a long, attenuate non- muscular bladder dorsal to the posterior genital apparatus. It does not pair but gives off a single median longitudinal vessel, which proceeds forward to the midacetabular region, where it gives off the transverse vessel. The median longitudinal trunk then runs forward to the origin of the ceca. Here it gives rise to three antero-lateral vessels. These bend outward and backward, with numerous anastomoses, and finally imite with the lateral traces of the trans- verse vessel. The outer reaches of the transverse vessel give rise to many anastomoses which are conspicuous in the postero-lateral portion of the body. The fundamental vessels of the holostome tv-pe are the paired laterals and the transverse vessel. Anastomoses and modifications have altered the system appreciably, but not beyond the ability to recognize in them a conmion type underlying the system, probably reducible to the Y-type of the distomes. The entire system contains many mediimi-sized refractor\' granules which oscillate back and forth thru the vessek at every movement of the animal. By imusual contraction of the worm, the granules are forced into the bladder and out thru the excretor}^ pore. C. Distomata. The distome cercaria has a simple type of excretory system, consisting of a posterior median bladder with two lateral longitudinal vessels in the body of the cercaria and a median longitudinal vessel in the tail. 1. The xiphidiocercariae. The excretory system of the stylet cercariae consists of a bladder, usually muscular, and a pair of lateral longitudinal vessels which arise from lateral cornua of the bladder. The primitive lateral system consists of three tubules, which emerge from the common lateral soon after the latter leaves the bladder. One of these tubules proceeds posteriad, while the other two run forward as inner and outer tubules. The single median tail vessel ends blindly near the posterior end of the tail; it sometimes receives tributaries, but this is not always the case. The bladder is a median posterior structure opening to the exterior thru the dorsal pore. It is usually muscular, unpaired. It v^aries greatly as to size and shape. It may be p3Tiform (Fig. 90), obo\^te (Fig. 93), crenate (Figs. 55, 81), truncate or obtnmcate (Figs. 60, 100), falciform (Looss, 1896, Fig. 146), or lunar (Looss, 1896, Fig. 179). The physiological and morphological bladders are not always the same. The former may encroach on the lateral tubules in order to increase its capa- city. This may consist of mere enlargements of the cornua without any change in structure (C glandidosa, Fig. 60; C micropharynx, Fig. 90). On the other 391 LIFE HISTORY OF TREMA TODES—FA UST 39 hand the needs for a muscular enlargement sometimes cause the musculariza- tion of the cornua (C. dendritica, Fig. 81; C. crenata, Fig. 55; and C. racemosa, Fig. 100). In C. diaphana (Fig. 76) the modification of structure has taken place before the enlargement of the long median vessel and the lateral tubes. The capillaries tributary to the lateral tubules are represented in their most simple form in C. micropharynx. The internal anterior vessel may move forward, as in C. crenata, or become rudimentary, as in C. glandulosa. The external anterior tubule is usually the most fully developed. It is important to note that the lateral systems of the xiphidiocercariae never anastomose or coalesce in any way. Thus the median sagittal plane acts as a "watershed." In the forms studied no large flame cells were found in the course of the ex- cretory system. If any minute flame cells were present they were concealed by the thick integument. The literature shows a paucity of observations on the flame cells of larval and adult distomes. Ssinitzin (1905) shows the details of the flame cells in Gorgordera pagenstecheri and in Phyllodisiomum folium. They consist of an ameboid cytoplasm in which is imbedded a spheroid nucleus with rich chro- matic inclusions. This cell is the terminus of the capillary (cl). It is ordi- narily funnel-shaped, but when distended becomes deeply reniform. The junction of the flame cell and the capillary is marked by a considerable number of cilia which vibrate rythmically, giving rise to Ssinitzin 's characterization, "vibratile tip cell of the excretory system." A detailed study of the flame cell of the adult distome is given by Looss (1896:110; Figs. 72, 77) for Distomum sanguineutn Sons. The details of the cell per se are not appreciably different from those given by Ssinitzin, but the distribution of the flame cells thru the body of the distome is described. There are four symmetrically paired groups of three cells each in the middle of the body, and one pair of two cells each in the anterior and posterior reaches of the body, making sixteen pairs of flame cells and capillaries in all (Fig. 77). This probably gives an indication of the arrangement of the flame cells in the typical distome. In Distomum isoporum (Looss, 1894, Fig. 103) six paired groups of ultimate tubules are figured with four flame cells to each group, making forty-eight flame cells in all. In Distomum cylindraceum (Fig. 163) there are six paired groups of capillaries with three flame cells to each group, totalling thirty-six flame cells. Thus the number of flame cells is not constant in different species but ordinarily remains constant for each species. Looss (1894:249, 250; Fig. 186) suggests that the fundamental larval system is the fundamental system of the adult. Extension and modification occur thru a dichotomy of the existing capillaries and flame cells, and an encroach- ment of the tubules upon the capillaries. The greatest modification takes place during encystment, altho this is in no sense a metamorphosis. Among adult American distomes the excretory system of Microphallus opacus Ward alone has been worked out with the exactitude of the Euro- pean workers (Wright, 1912, PL 17, Figs. 1, 2). This form has the distome 40 ILLINOIS BIOLOGICAL MONOGRAPHS [40 Y-shaped bladder and cornua. There are only eight paired capillaries, and only sixteen flame cells. This condition constitutes a reduction of flame cells from the average types, a reduction which can not be entirely accounted for by the small size of the species. 2. The Echinostome type. This family of distomes is characterized by simplicity of detail in the excretory system except at the head of the main lateral vessel. The bladder is not markedly muscular. The pair of lateral vessels arise from the anterior median region of the bladder, and not from the horns of this vesicle as in the xiphidiocercariae. The main trunks do not divide but proceed to the cephalic extremity along the lateral margins. They sometimes receive small tributaries along their course. In the cephalic region the vessel commonly flexes back on itself. Such flexure may continue back to the posterior extremity of the body, as in C reflexae (Cort, 1915, Fig. 43), or may continue caudad only a short distance, reflexing a second time (C. biflexa, Fig. 135). An intermediate form, C. echinata, has been described by Looss (1894:191), where the first flexure continues caudad while another part is reflexed cephalad. A modification of the type represented by C. biflexa, where the double flexure is entirely within the cephalic region, is seen in C. trisolenata (Fig. 109). Either the end of the flexure has been fused to the most anterior part of the main vessel, or the middle portion of the system has been modified. As a result a triangular channel system has been formed at the anterior end of this excretory system. The characteristic feature of the excretory system in the two species of echinostomes is the triplet of flame cells at the anterior part of the system. A detailed study of the flame cells in C. biflexa is found in figure 138. The cells are situated in the pockets communicating with the ultimate part of the re- flexed tubule. Cell a is found in the sinus between the secondary and tertiary vessel. It points upward and outward. It is the smallest of the three cells. Cell c occupies the swollen end of the tertiary vessel. It is the largest of the three vessels; its ciUa are the most rythmical of the group. Cell b Hes midway between cells a and c. It points downward and inward. Cells a and b func- tion in bringing the excretory wastes into the vessel from the surrounding tissue and cell c directs the excretory material along the vessel. The excretory system of certain species of echinostome cercariae contain granules. These granules have been found in all C. trisolenata examined; they are found in the lateral vessels from the region of the pharynx posteriad to the acetabulum. They have not been seen in C. biflexa. The excretory system in the tail of echinostome cercariae is not uniform. In C. trisolenata there is a single median tube with no prominent tributaries. In C. biflexa a median tube runs two-fifths the distance posteriad, where it divides to form two tubules which proceed distad. In C. trivohis and C. reflexae (Cort, 1915, Figs. 39, 43) the median vessel of the tail courses back- ward about one-fifth way and ends there in a bifurcation, the ends of which 41] LIFE HISTORY OF TREMATODES— FAUST 41 open to the sides. The hiflexa type seems to be intermediate between the echinostome type described by Cort and the more common distome type. It is highly probable that the excretory system of the echinostome, with three flame cells in the anterior portion of the system and possibly several smaller ones further caudad, has arisen from the primitive distome type. In most cases, the posterior flame cells have become fused into larger ones, so that only three flame cells remain in the anterior part of the system in C. trisolenata and C. biflexa. 3. The Furcocercaria type. The mature apharyngeal distome cercaria of the furcocercous type (i.e. schistosome) has a very small bladder in the posterior part of the body and two lateral vessels running cephalad. The unpaired portion of the tail has a single median canal, which is united to the system of the trunk thru an "eyelet anastomosis." The median tubule of the tail forks to enter the rami. The origin of the caudal vessels has been worked out by Looss (1896, Figs. 172-174) for C. vivax Sonsino. These tubules arise as the posterior extension of the paired body excretory tubes. Their fusion in the common portion of the tail occurs after the rami have become well differentiated. The "eyelet" is an index of the original paired system in both body and tail. A study of the species C gracillima (Fig. 143) and C. tuberistoma (Fig. 155) shows the main features of the vivax type. The small bladder, the lateral canals, the median caudal tube, bifurcating distally to proceed into the rami, the "eyelet" at the junction of the body and the tail — all of these seem to be constant for the entire group. Beyond these characters the features of the several species are divergent. In C. gracillima (Figs. 143, 145) the caudal portion is extremely simple, containing only the common median tubule and the forked tubule system entering the rami. Unlike C. vivax with its three pairs of flame cilia in the common caudal tubule, this species has no flame cells in the caudal portion of the worm. The system in the body of the cercaria has a non-muscular trilateral bladder, small posterior tubes arising from the lateral tubes, and a ciliary pocket about one-fourth way from the posterior margin of the body, on the inner wall of each lateral tube (Fig. 145). At the posterior margin of this ciliary pocket small tributary canals from the median plane flow into the main canal. Slightly cephalad is another pocket, somewhat larger than the ciliary pocket, filled with small granules of various sizes and shapes. Into this pocket four or five small canals empty, the median ones of which anstomose with their mates from the opposite side. No ciliary cells have been found in the terminations of the capillaries. In C. tuberistoma the caudal portion of the worm is characterized by five transverse canals. Another pair, anterior to these, is conspicuous because it runs forward for a short distance and is then reflexed backward for some distance (Fig. 155). The eyelet and the bladder are both muscular. In the body portion there are no pockets for the lodgement of granules and no transverse anastomoses. No flame cells have been found in this larva. 42 ILLINOIS BIOLOGICAL MONOGRAPHS f42 A comparison of the furcocercous larvae with the Schistosomatidae shows the striking similarity of the excretory systems of these forms. Looss (1895) finds the system of male and female Schistosoma haematobium alike, altho that of the female may be sUghtly better developed, due to a minimization of the musculature. The bladder is median, non-muscular, except for a weak sphincter at the pore. It receives the two longitudinals at its antero- lateral reaches. There is no median canal (p. 72). Many of the laterals are dendritic, altho they do not anastomose. Small flame ciMa are at the heads of the capillary tubes of Sn to 4/1 diameter. These flame cells and capil- laries are intra-cellular, and not surrounded by an epithelial lining. D. Excretory system of the Parthenitae. Details are given only in ob- servations of Looss (1892:158-161) for the excretory system of young parthe- nitae. The "protonephridia" of Ssinitzin (1911:77-80; PI. 1, Figs. 24, 25), described by him in connection with the birthpore of the redia, have not been proved to have an excretory function. According to Looss the excretory sytem both in the sporocyst and redia arises as a paired structure, from which capillaries and flame cells soon arise. The observations of the writer have been confined to the adult sporocyst and redia of the species studied, in which the system is strikingly different from the embryonic condition. In many cases the excretory system consists of a diamond pattern of intercellular channels, without any clue to the former bilateral symmetry. The same amount of modification holds for both sporo- cyst and redia. Even in the holostome redia (Fig. 42) this diamond pattern is found. No flame cells have been found in adult parthenitae. This distinct modification of the excretory system in parthenitae is not surprising in view of the extraordinary degeneration of the animal that has resulted from its endoparasitic habits during its entire life. Excretory granules. The excretory granules of the cercaria and parthenita are spheroidal and have the general appearance of glass beads. Their re- fractive index is very high. The size of the concretions is variable in different groups and even in the same individual. As a rule the granules are largest in the monostomes and holostomes. Few writers have given consideration to these excretory granules. Thomas (1883:117) says for Fasciola hepatica larvae that "the yellowish granules. . . appear to be excretory products formed within the cells of the sporocyst and then ejected. They are partially soluble in acids, leaving an organic basis. " Looss refers to them as opaque concrement-granules which on first sight throw the boundaries of the tubules into black rehef (1894:165). They are insoluble in alcohol and color beautifully in stained mounts. Reference is made to these granules by Cort (1915:16) to the effect that the tubules of the mono- stomes are filled thruout their entire length "with small round concretions which disappear in the process of preservation." The writer has found that these granules are not usually preserved in the corrosive-acetic fixing fluids. However, if fixation is done without the acid fraction of the fluid the granules 43] LIFE HISTOR Y OF TREMA TODES—FA UST 43 are preserved. Application of strong acid to the granule causes an evolution of gas. The granules are negative to inorganic CO2 tests, and are non-crystal- line, as determined by the petrographic microscope. They take hematoxylin stains readily, altho they do not stain deeply. They give no Molisch reaction. The xanthroproteic test is positive, indicating a benzene nucleus. It is probable that they consist of a conjugate protein before fixation. Fixation with mercuric chlorid alters them, since they are then acid and alkali re- sistent. Generalizations on the excretory sytem. The excretory system of the trematodes, including both cercariae and parthenitae, is essentially a bilateral system. It arises as two paired tubules, which fuse in the bladder region of the cercaria to form the vesicle. The mature system of the parthenitae is highly modified from the primitive type. The system as found in the cer- caria is carried into the adult without very profound modification. Most individuals of all generations contain within their excretory systems spheroidal concretions, which are waste organic products, quite probably derived proteins. They lodge in the main tubes and are expelled thru the excretory pore. DIGESTIVE SYSTEM The most uniform system in the Digenea is the digestive tract. With the exception of the sub-order Gasterostomata and the super-family Prostomata, the enteric canal is triclad in character. The main features of difference in the various families of the group is the modification of the esophagus region of the gut. In most forms there is a pharynx sphincter just within the oral pocket. In other species the pharynx is small and inconspicuous. In still others there is no bulbus around the esophagus, but in its stead a group of gland cells. The digestive system in the cercaria is not distinctly a larval system but practically a fully matured system. In some cases it is not functional, as in the Monostomata, where the paired ceca are still filled with a jell (Fig. 13) ; in the Schistosomatidae there is the interesting phenomenon of short ceca in some species {Cercaria gracilUma) and entire absence in others (C tuheristoma) . While the larval digestive glands of the cercaria may not be retained or may be metamorphosed in the mature worm, nevertheless they are functional in most larvae. The forking of the ceca is not constant, varying in different species. Even the relative length of the parts of the tract varies greatly in the same individual at different times, due to the extreme limits of contraction and expansion of the larva, so that this relation of parts can not be entirely depended on as a basis for diagnosis. As a whole the digestive tract is remarkably uniform and simple, which might be expected in a larva in which the food supply is so accessible. The sporocyst has no digestive tract, but takes its nourishment directly thru the body wall. In consequence the cells of the epidermis are thin and at times apparently glandular, as in the stylet cercariae. 44 ILLINIOS BIOLOGICAL MONOGRAPHS [44 The redia has a gut-pouch for a digestive system, with a pharynx sphincter around the anterior end. Hence the epidermis is not used in the capacity of food transference, and is heavily Kned beneath with an integvmientary secretion. For securing food the redia of Cercaria pdlticida is provided with an oral piercing organ. The redia of C. flabelliformis is equipped with paired mucin-salivary glands. GENITAL SYSTEM This system of organs has been the most constant basis of classification of adult trematodes. It is also the best specific criterion for the larvae, altho a more deUcate technic is required for differentiation of the genital organs in the cercaria than in the adult worm. Because these organs have failed to come out in the ordinar>^ preparations, no attempts have been made to use them as basis for correlating larvae and adults. Cell masses have been figured by Looss (1896), Ssinitzin (1905, 1911) Miyairi and Suzuki (1914) and Cort (1915), but these workers have not in any case showTi them in detail. By means of a lengthy staining in a weak solution of Delafield's hematoxylin, followed by rapid differentiation and then neutralization with potassium acetate solutions in the higher alcohols, the genital organs of the cercariae have been traced with a degree of detail not previously attained. These organs have been found to offer valuable data for correlating cercariae and adult trematodes. A. Monostomata. All three species of monostomes on which observations have been made, Cercaria pellucida, C. kanadensis, and C. urbanensis Cort are characterized by the symmetrically arranged testes, the presence of Laurer's canal, the location of the vitelline glands in a double series on each side of the body, and the courses of the uterus and vas deferens. Ssinitzin (1905, Fig. 76) shows the inner series of five paired vitellaria for C. ephemera Nitzsch, but he has figured no outer series of three glands, such as are found in the three species worked out by the \NTiter. He is in error in considering them cj'sto- genous glands, because their connection is traceable thru filiform ducts to the ootype. All these species are provisionally referred to the Notocotyhdae. With the growth of the cercaria to the adult monostome the originally distinct and readily recognizable vitelline elements becomed fused in part. Looss 's figure (1896, Fig. 94) of Notocotyle verrticosa (Froel.) shows five rather poorly defined foci of vitelline elements in each of the lateral series. It is possible that the five inner elements of the series have become fused to the three outer elements of the series, thus causing the indefinite outline of the elements in the adult worm. The vitelline glands of Notocotyle quinqueseriale are ap- parently eight to the side. Here the three glands of the outer series may have been introduced between the five glands of the inner series (Barker and Laugh- lin, 1911, PI. 1, Fig. 10). A symmetrical pair of \dtelline ducts, between the inner and outer series of glands, leads to the ootype. The cercariae which the writer has studied in this group are readily dis- tinguished by a comparison of their genital systems. 45] LIFE HISTORY OF TREMATODES— FAUST 45 In Cercaria pellucida the well-developed cirrus pouch and the poorly de- veloped vagina reach the confines of the excretory trunk just behind the median eye. In C. konadensis the cirrus pouch and the vagina are both equally devel- oped. The former is falciform, the later pyriform. The vagina is lateral to the cirrus pouch but is somewhat posterior to it. The genital pore in C. pellucida is not as far posterior as that in C. konadensis. In this species, as well in C. urhanensis, the testes are marked by definite cell masses, while in C. konadensis the testicular masses are much more indefinite. They are small in each case and lie ventral to the vitelline organs. The course of the vasa efferentia is clearly outlined. On the basis of the structure of the vitellaria alone these species can be differentiated in the cercaria stage. In C. pellucida the glands are actually spiculate in outline, flattened dorsoventrally. The vitelline material is finely granular and closely massed. In C. konadensis the glands are decidedly dendritic, and the granules are diffuse. In C. urhanensis the glands are lobate and the fine granules are included within a dense mucoid matrix. B. Holostomata. The genitalia of the Holostomidae and Hemistomidae will be considered separately. 1. Holostomidae. The thickness of the tetracotyle larva, together with the thickness of the cysts, in which the majority of these individuals have been found, has prevented a study of the genital system from stained toto mounts. However, these organs come out clearly in frontal sections of 7/i thickness (Fig. 39). In Cercaria flabelliformis the ovary is situated just caudal to the posteriormost muscular lappet. A short oviduct proceeds dorsad to the ootype. The uterus winds posteriad to the genital pouch. The vitelline glands are long paired cords. In C. flabelliformis they are composed of large vesicular glands (Fig. 39) ; in Tetracotyle pipientis (Fig. 47) they are loosely follicular. The testes are paired structures which may occupy positions from the plane of the ovary (T. pipientis) to the plane of the genital pouch (C. flabelliformis). The pouch is muscular and opens posteriad, ventral to the excretory pore. Thus these genital organs are tj^ically holostome in character, correspond- ing to the main features described for the adults by Brandes (1891), Thoss (1897), and Johnston (1904). They are sufficiently detailed in this stage of the species development to be of diagnostic value. 2. Hemistomidae. In this family all of the genital organs are situated entirely posterior to the acetabulum. The primitive genital pore, anterior to the acetabulum, has lost its connection with the genitalia, and with the addition of muscular elements has assumed a suctorial function. The species Cercaria ptychocheilus has an ovary elongate in a transverse plane, nearly spatulate, situated just behind the acetabulum. It is granulate, compact, and stains deeply with hematoxylin dyes. At its left it merges into the oviduct, a large coiled tubule, which bends on itself three times just behind the margin of the ovary, then empties into the ootype just anterior 46 ILLINOIS BIOLOGICAL MONOGRAPHS [46 to the bursa copulatrix. The densely massed cells of the glands in the vicinity of the ootype lie just above this organ. The testes are situated at the right side just ventral to the ovary. They are small compact glands, and have no ducts at this stage of development. The vitelline ducts from the diffuse vitelline follicles meet the other genital products in the ootype. The genital bursa is very large and muscular, and hes just ventral to the excretory bladder. Symmetrically arranged glands, with glandular nuclei and hyaUne cytoplasm, empty into it from the postero-lateral reaches. They vary in number from seven to ten on each side. With the exception of these glands emptying into the bursa, all of the genital organs of this larva lie in the anterior patelliform region. With the exception of the later formation of a uterine duct between the oot}^e and the bursa, all of the organs are in the approximate location where they wUl be in the adult worm. The massing of the organs in the anterior portion of the animal is undoubtedly correlated with the abbreviation of the appendicular portion of the species. The literature on larval hemistomes (Diplostomulum) shows that von Nordmann (1832:34-35, PL III, Fig. 1) has described an egg pouch for D. volvens and two symmetrically arranged testes, with ducts, in the region of the acetabulum. Leidy (1904:111) describing D. grande (Diesing), speaks of "ovaries, dusky yellow." Since the ovary in the Holostomata is single, the organs thus described are possibly testes. The bursa is the muscular organ par excellence in Cercaria ptychocheilus. Muscle elements protrude into the atriiun, so that a constriction exists between the anterior and posterior portions of the organ. The genital systems of the holostome and the hemistome are similar in those features in which they differ from the distomes. They have modified their primitive genital pore so that it has either become rudimentary or has as- sumed a muscular function. The sperm ducts and the uterine duct empty into the pouch at the posterior end of the animal, instead of the atrium an- terior to the acetabulum. The new genital p)ore is posterior to the ootype, and ventral to the excretory pore. C. Distomata. The genital organs of the distomes are different in various families. 1. Xiphidiocercariae. The genital organs in these cercariae are readily defined with reference to the acetabulum. They are mostly situated in the middle of the ventral side of the larva just behind the acetabulum or shghtly posterior to this position. The ootype is posterior and dorsal to the acetabulum. The uterus coils around the right side of the acetabulimi. It ends in a blimt or tapering ceU mass. Laurer's canal is on the left of the median line, just behind the middle of the acetabulum. It is present in all of the species of stylet cercariae examined. Only in two species are the testicular cell masses outlined. In C. crenata (Fig. 59) these glands consist of two large ovate masses. 47] LIFE HISTOR Y OF TREMA TODES—FA UST 47 In C. dendritica (Fig. 86) the testes are small, situated closely behind the oo- type. In no case is the ovary clearly differentiated from the region of the 00 type. The vitellaria are definitely outlined. These glands in C. glandulosa (Fig. 66), C. diaphana (Fig. 78), and C. micro pharynx (Fig. 96) are much more alike than those in the remainder of the stylet species. The vitelline follicles of C. dendritica (Fig. 86), and C. crenata (Fig. 59) are noticeably dissimilar, having on the one hand, a system extending the entire length of the body, and, on the other hand, a system confined to the immediate vicinity of the ootype. The genital organs and ducts of C. racemosa, the lateral fin type (Fig. 104), bear some resemblance to those of C. dendritica (Fig. 86). However, Laurer's canal is very prominent in this fintail species, while in C. dendritica it is not so prominent. Instead of coiUng around the right side of the acetabulum, the uterus in C. racemosa makes four double obHque coils dorsal to the acetabu- lum. The ovarian cell mass is dorsal to the ootype and connects with that organ thru a short duct. The testes masses have not been observed. 2. Echinostomidae. The two species of this group which have been studied, C. trisolenata and C. hiflexa, vary in the structure of their genital organs most markedly. In view of this diversity it does not seem advisable to take them up in detail in this comparative phase of the study. 3. Furcocercariae. The material of Cercaria gracillima was studied with especial reference to the genital cell masses, both in the totos and the section mounts. The main system consists of the ovary-uterus mass on the right and the cirrus mass on the left, both in the vicinity of the acetabulum. The vitellaria are lateral and empty into the ootype thru transverse ducts (Fig. 149). The testicular follicles are numerous, 24 or 25 having been counted. They are proUferated from a posterior germ mass, which is ventral to the bladder NERVOUS SYSTEM One of the earlier and better known system of the adult trematode was the nervous system. Leuckart (1863:462) states that Bojanus and Mehlis were famihar with the gross anatomy of the nervous system of the larger flukes, and that von Laurer, Diesing and Siebold as well as the elder van Beneden were acquainted with the nervous systems of both large and small worms. Leuckart described the sy tem for Fasciola hepatica and Dicrocoelium lanceatum-. He states that there are two or three stems, the anterior dorsalis and an- terior lateralis and the thick posterior ven trails. Somewhat later Lang (1880: 46-50), substantiates the work of Leuckart and, in addition describes the dor- sal posterior and acetabular innervation. Gaffron (1884) and Looss (1892, 1894, 1895) have placed the nerve anatomy of the adult trematode on a firm foundation. Hofmann (1899), Wright (1912), and Monticelli (1914) have confirmed the work of earlier workers. Nor has the finer work on the nerve endings and the ganglion cells been overlooked. Many of the earlier writers 48 ILUNOIS BIOLOGICAL MONOGRAPHS [48 made out the ganglion cells of the pharynx region and recorded their ob- servations on the nuclei. Bettendorf (1897), working on Fasciola hepatica with intra vitam methylene blue and Golgi methods, has brought out clearly and convincingly the nervous sytem of this worm. This study has been aug- mented by the work of Zailer (1914). In view of the extensive study of the nervous system of the adult tre- matode, it is a matter of no Httle surprise that so Uttle has been done on the nervous structure of the cercaria and the parthenita. Looss (1894:245) has confessed the difficulty in making such a study and had observed that "ein, wie es scheint, nicht unbetrachtUcher Theil derselben fallt in die Zeit der Cercarienentwicklimg, imd weiterhin, ist auch der ganze Apparat wahrend seiner AusbUdungzeit, dass es mitimter recht schwer ist, zu entscheiden was zu ihm und was zu dem umgebenden Parenchyme gehort. " However, Looss depended on Hving mounts for his study and did not use preserved material or avail himseh" of intra vitam methylene blue technic. By the use of an eosin coimterstain against a hematoxyhn background the writer has been able to secure remarkably clear sections showing with extraordinary deUcacy the nerve branches as well as the central nervous system. It is the purpose of this section of trematode morphology to present data and observations on the development and structure of the nervous system in parthenita and cercaria. The central nervous system of the adult trematode consists of two central ganglion masses, situated dorsal and lateral to the pharynx and yoked together by a transverse commissure passing dorsal to the pharynx. The appearance of this structure has been aptly described by Lang (1880:46) as a saddle between oral sucker and pharynx. In cross section it is lunar. Here are centered the most of the gangUon cells, altho they are frequently found poster- iorly, and often in the sensory apparatus of the oral and ventral suckers. The system also has a subesophageal commissure which differs in size and shape in different species of flukes. Extending forward into the region of the oral sucker are three pairs of nerve trunks, the dorsalis, lateraUs, and ventraHs. Of these three the latter is the most fully developed. It has a ramus muscular- is which is both motor and sensory (Zailer), and an extensive connection with the oral ner\'e ring. The anterior laterahs is also a strongly developed trunk, with a ramus muscularis and a ramus palpaUs, and transverse commissures to the anterior dorsahs and posterior lateralis. The anterior dorsaUs is a weakly developed nerve which innervates the apical sensory field. A trans- verse commissure connects the two dorsales above the head muscle sheath. In addition to these three primary trunks, the palatinus, a weak motor nerve, lies internal to the anterior ventrahs. Posterior to the central nervous system are the three posterior trunks, the dorsahs, laterahs, and ventrahs. The ven- tral trunk is by far the most strongly developed. In addition to these is the small but conspicuous internal branch of the ventrahs known as the pharyn- geahs. It occupies a posterior position, corresponding to the palatinus anter- ior to the central nervous system. 49J LIFE HISTORY OF TREMATODES— FAUST 49 Braun (1893:683) considers the ventralis, dorsalis, and pharyngealis to be the three pairs of posterior nerves. However, the consistent course of the lateralis to the posterior extremity of the body, its early appearance in the embryology of the worm, and its conmiissural connections with the anterior lateralis and posterior dorsalis surely prove its right to a place in the rank of the primary posterior nerve trunks. The nervous system of the monostomes has been worked out by Jager- skiold (1891) for Ogmogaster plicatus (Crepl.), and by Monticelli and Looss for Catatropis verrucosa (Frol.). Looss (1896:149) considers the system similar to the distome type. "Je n'hesite pas a attribuer au systeme nerveux de notre ver une construction analogue a celle que nous avons deja signalee chez un bon nombre de Trematodes digeneses." However, Looss (1896:11-16) was not able to make out clearly the anterior trunks. Jagerskiold (1891 :14-16) describes the cerebral ganglion masses with the transverse commissure, the posterior ventralis, dorsaUs, and lateralis, and the three anterior trunks, short and thorn-like, the homologs of the dorsalis, lateralis, and ventralis. A stem, designated as the "fourth," arising from the anterior reaches of the cerebral masses, passes ventrad to the region below the oral sucker; it seems probable that it is the palatinus. The only real modification from the distome type is the absence of the acetabular innervation, due to the loss of this organ. In the Amphistomata adults among the earlier writers Lejtenyi (1881 :142- 144), working on Gastrodiscus polymastos Leuck!, described two ganglion centra with the dorsal commissural bridge, but with only one anterior and one poster- ior pair of trunks. In contrast to this incomplete description is that given by Looss (1896:21, 22) for Gastrodiscus aegyptiacus (Cobb), where the usual distome nerve trunks, were found, and, in addition, a median anterior and a median posterior nerve. Looss has worked out the nerve anatomy for Am- phistomum suhclavatum Rud. in even greater detail (1892:151; Taf. 19, Figs. 1, 2, ), and finds that they correspond to the distome type, except for the innervation of the posterior sucker. The one group of the Digenea where the nervous system has been almost entirely neglected is the Holostomata. Brandes (1891) states that none of the workers of the nervous system up to his day have worked on the holosto- mids. He has observed only the central nerve center lying above the posterior portion of the pharynx, an anterior and a posterior pair of nerve trunks, the tracings of which he has found in sections. Thoss (1897), working on Holo- stotnum cucullus, finds the main nerve center lying dorsal to the origin of the esophagus, with two pairs of anterior and one pair of posterior nerve trunks. The central nervous system of Cercaria trisolenata, the echinostome, consists of two masses of ganglion cells and the dorsal commissure lying con- cavely on the dorsal side of the large muscular pharynx. The commissure is broad and flat. The dorsal surface of the gangUon masses and the commissure present a smoothly curved surface, but on the ventral side the ganglia bulge out against the pharynx. The anterior trunks consist of the dorsalis, lateralis, ventralis, and the palatinus. The paired dorsales arise together with the 50 JLUNOIS BIOLOGICAL MONOGRAPHS [SO laterales and proceed forward with them for some distance. After separation, the dorsalis runs more median, then flexes outward and dorsalward over the oral hood, proceeding toward the apical sensory center. The lateralis at the point where it leaves the dorsalis proceeds outward and forward, so that it reaches a level slightly below the plane of the central nervous system. SUghtly after diverging from the dorsaUs the lateralis gives back a commissure to the dorsalis. This dorsolateral connective fuses with the dorsaUs just behind the posteriormost branching of this trunk. Arising from the most ventral reaches of the gangUon center is the ventralis, a broad flat trimk, which courses outward and downward to the oral Hp of the oral sucker. Internally it gives oflF the palatine, which Ues just lateral to the pharynx. Caudal to the central nervous system arise the four pairs of posterior trunks, the dorsales, the laterales, the ventrales, and the pharyngeales. The dorsaUs branch arises dorsal and slightly lateral to the junction of the gangHon and the commissure. It runs straight backward, slightly dorsal to the plane of the central nervous system. The lateralis arises sUghtly lateral to the dorsaUs; its path Ues outward and backward. The ventralis arises from the very heart of the gangUon mass. It spreads outward and then runs back- ward paraUel to its mate. The ventral commissure, arises just median to the origin of the posterior ventraUs flexing below the prepharyngeal opening. It is stout and bowed considerably downward. Between the commissure and the ventraUs arises the pharyngeaUs. In a germ ball of Cercaria trisolenata some 45^4 by 60ai in size, the central nervous system is weU developed. This may be called the butterfly stage (Fig. 121). At this period there are two pairs of main tnmks anterior and four pairs posterior to the central gangUon mass. The anterior trunks are the ventrales and the laterales. By reference to the next stage in the devel- opment (Fig. 122), the dorsales are found to arise from the sinus between the laterales buds of figiu-e 121. They arise at first as a single bud and bifurcate later. CaudaUy the most conspicuous trunks are the dorsales, which arise in a median plane and conspicuously dorsal to the other posterior trunks. The dorsal commissure at this period is practicaUy negligible. The outer- most ventral tnmk-buds are the laterales, short and stubby at this period of growth. The ventral trunks arise from the ventral portion of the cerebral masses. Between them and the laterales arise trunks which are present in the embryonic stage only. They may be designated as the posterior intermedins nerves. In stage 11 (Fig. 122) a very decided change has occurred in the outline of the central nervous system, altho the fundaments of the first stage described are present. Anteriorly the intermediate space between the laterales has disappeared and from that region has arisen a wedge which is the fundament of the paired dorsales. The ventral trunks have been set off to themselves by a lateral growth and elongation of the intermediate fibers. On the caudal side of the gangUon the posterior dorsalis has been separated frorn its mate by the growth of the dorsal saddle commissure. Most noticeable, however, is the 51] LIFE HISTOR Y OF TREMA TODES—FA UST 51 change that has taken place in the ventral portion of the system. Here the space between the ventrales has become exceptionally wide and a prominent commissure has grown out from the trunks, commonly known as the subesopha- geal commissure. It is the homolog of the transverse commissure occuring along the entire ventral side. The intermedins trunk has become fused with the posterior lateralis, in part, and then crosses over to the ventralis. This is the connection known in adult nerve anatomy as the ventrolateral com- missure, a strong and important intercommunicating trunk (Fig. 123). In the developmental stages no trace of palatinus or pharyngealis has been found. Cercaria glandulosa, a xiphidiocercaria, is favorable material for the study of the minute structure of the nerve fibers and endings. In the anterior end of this larva there occur in five frontal sections of 8/i thickness all of the fundamental nerve endings of this region. In section 1 of the worm (the most dorsal section), there are no nerve structures save a few sensillae to the dorsal lip of the oral sucker. They receive innervation from the anterior dorsalis, and derive that innervation from the anteriormost fibers seen beneath in section 2, just in front of the musculuspreoralis. Section 2 (Fig. 68) shows the trunk of the dorsalis descending into the oral musculature. It has three main branches, one coursing to the preoral region to supply the conductive strands for the preoral sensory endings, one becoming the short superficalis, and a longer one, the profundus, passing under the endings of the superficialis. In the region of the musculus preoralis, the apical sensory field is continuous across the sucker from right to left. In section 3 (Fig. 69) are illustrated the main outlines of the central nervous sytem, together with the anterior trunks. Here is the dorsal portion of the gangUon cells. Anterior and dorsal is the dorsal commissure and ventral is the subesophageal commissure. The for- ward traces are the trunks of the laterales with the outermost superficial ramus palpalis and the more deeply situated ramus muscularis. The latter branch innervates the musculus preoralis and the anterior lip of the oral sucker. On the left is the trunk of the anterior ventraHs, arising from below the mass of the ganglion cells. At the anterior extremity is the apical sensory field. The dorsolateral commissure is very clearly shown in this section. Section 4 (Fig. 70) shows the remainder of the central gangUa with the left anterior ventralis passing forward. This is a large trunk, with an especially important ramus palpalis leading to the apical sensory field, and a small oral nervus communicans supplying the oral nerve ring. This ring completely encircles the superficial region of the oral sucker and connects with the superficial branch of the dorsahs. The ramus muscularis of the ventralis and the palatine branch of the ventraHs are found in section 5 (not figured). Passing caudad all the posterior roots are well defined. Four posterior roots are visible in section 3 (Fig. 69). These include the posterior dorsales, laterales, ventrales, and pharyngeals. In a fortunately cut section of the same species the innervation of the acetabulum is beautifully demonstrated (Fig. 71). The two main longitudinal trunks, the ventrales and the laterales, 52 ILLINOIS BIOLOGICAL MONOGRAPHS [52 are connected by commissures. Those around the acetabulum are of especial importance. The preace tabular commissure arises from the lateral trunk and proceeds in a posterior oblique course, then around the anterior reach of the acetabulum to meet the branch from the other side. The postacetabular branch arises from the lateralis also, but continues caudad along the course of the ventralis. Behind the acetabulum it meets the branch from the oppo- site side to form the span. From these trunks circumscribing the acetabulum two ring commissures arise, a superiicialis and a profundus, of which the latter with the nerve endings is found in the section (Fig. 71). The nervous system of the monostome, as worked out by Jagerskiold (1891, Taf. I) for Ogmogaster plicatus (Crepl.), has been substantiated for the most part in the study of Cercaria pellucida (see figure 23). The three paired posterior trunks are evident. The posterior ventralis is the most important of these and can be traced to the caudal extremity of the animal in all cercariae of this species, as well as in C. konadensis and C. urhanensis. The dorsalis is less conspicuous, yet it is usually traceable far caudad. The posterior lateralis is delicate. It arises near the origin of the ventralis and swings out laterad in a great bov/. It, too, can usually be traced to the posterior extremity of the body. The anterior trunks can also be definitely traced. The ventralis arises from the extreme lateral horn of the ganglion center in conjunction with the posterior ventralis. More median, the anterior lateralis is found. The two anterior dorsales arise as a single structure along the median line. Their primary function in the cercaria is the innervation of the median pigment eye, altho branches may be traced farther anteriad. Likewise, an important branch of each posterior dorsalis constitutes the nerve tract to the lateral eye. The ganghon cells in the monostomes are superficial to the nerve strands. A considerable number of them are not even in intimate contact with the fibers, but have fibrillar communications with them. The ganglion masses from which the nerves arise are distinctly cornuate, with a wide dorsal com- missure. Pigmentation and eye-spots in the monostomes. The monostome cer- cariae that have come under the direct observation of the writer, together with those described in the literature, may be placed in two groups according to their eye-spots, namely, those with a single pair of eye-spots, disposed laterally to the brain center, and those with an additional median eye, anterior to the central nervous system. The amount of pigmentation is considerably larger in the trioculate species than in the binoculate type. Figures 1 to 3 show in dorsal view a series of stages in the pigmentation of Cercaria pellucida. The pigment originates anteriorly over the brain center and proceeds caudad along six lines of growth. A very careful study of the pigmentation in these species indicates that a very simple but reasonable relation exists between the pigmentation and the underlying nervous system. The pigmentation is found to be a delicate superficial index of the underlying nerve fibers. This 531 LIFE HISTOR Y OF TREMA TODES—FA UST S3 pigmentation is present in the subintegumentary areas and follows with pre- cision all the ramifications even to the nerve endings. Figure 37 shows the nerve endings in the anterolateral reaches of Cercaria pellucida. In the paired eye-spot a definite subspherical "lens" is found in the region of the concentration of the pigment. In the median eye of the trioculate type a "lens" is sometimes present. The origin of the eye is simple. At an early stage in the germ ball (60 n to 80 ju), when the cell masses of the nerve trunks are definitely outlined as they emerge from the ganglion center (Fig. 36), a branch of the posterior dorsalis, larger than any other nerve, pushes out obliquely. It meets an invagination of the ectodermal layer, which may be considered an "optic cup." There soon forms in the hollow of the cup a group of dark brown refractory granules, which entirely lines the optic cup several layers deep and leave but a small cavity within. The optic branch of the dorsalis bends back into the cavity at the place where it first comes in contact with the cup and here ends in a pyriform enlargement, the nerve cell. The structure of this end organ is such that it might be interpreted as a " lens, " if the connection with the nerve is not made out. Cort (1915:15) has placed that sort of an interpretation on the eye structure of C. urbanensis and C. inhabilis. For the former he states that " each true eye is formed by a mass of pigment in the form of a cup, the bottom of which is thicker than the sides. A lens fits into the opening of the cup, leaving a space between its lower sur- face and the bottom of the cup." And again, for C. inhabilis, "the large eyespots . . . are composed of the lens and the cone of pigment like those already described for the monostome, Cercaria urbanensis.'' The writer has studied some of Cort's material and has found sections where such an inter- pretation might be made from a single section. But in the preceding or fol- lowing section the connection of this "lens" with the optic nerve is plainly seen. The eye structure as studied in this monostome is similar to that found in the Monogenea, especially the type in the posterior eye of Tristommn molae (Hesse, 1897:559; Taf. 28, Fig. 29). The nervous system of the monogenetic trematode was first studied in detail by Lang (1880), who made out the pigment cup, a refractory body (Uchtbrechender Korper), a ganglion cell, the retina, and eye muscles (p. 41; Taf. I, Fig. 2, Taf. II, Fig. 2). Most later investigators mention only theper- ceptory body and the accessory apparatus, altho Andre (1910:217) has iden- tified the muscle fibers of Lang. The writer believes that the movement of the eyes depends largely on the general bodily movement. In the adult Monogenea studied the pigment cup is found to lie between the refractory bulb of the eye and the possible source of light (Goto, 1894:81). In the monostomes, as in Dendrocoelium lacteum (Hesse, 1897, Taf. 27, Fig. 10), the hollow of the cup is directed outward, so that light falling on the eye must pass thru the end organ before reaching the inner portion of the pigment complex. The pigment of the organism is probably the waste product in the metabolic economy of the worm. Its close association with the nerve endings in the 54 ILLINOIS BIOLOGICAL MONOGRAPHS (54 monostome cercariae seems to indicate that it is the melanoidin fraction of the oxidative processes in the nervous system. The possibility of utility as a receptor of light or heat is a secondary item and must not be confused with the primary meaning of the pigmentation. In the free-Uving Platyhelminthes the fully developed eye is present in the mature individual. In the ectoparasitic trematodes the eye-spot is well developed in the young animal (Hesse, 1897:560, 561), but degeneration takes place as the animal matures. Goto (1894:81), speaking of Tristomum, ob- serves: "Morphologically speaking they are certainly degenerate eyes; and have probably been derived from such eyes as are found in Turbellaria; but I do not think they are functional. In the first place the pigment granules are situated on the dorsal side and thus prevent the light from reaching the lens, since the dorsal side is the only direction from which light can come. In the second place there is not always a distinct retina. If these 'eyes' are really still useful to the animal, they may possibly be a temperature sense organ; and for that purpose their structure seems to answer well." Goto goes on to show that the more degenerate condition of the eyes in Tristomum ovale is due to the greater degree of internal parasitism of this species than that of Tristomum molae. In the monostome, the eyes are well developed in the cercaria but become fully degenerate, with a loss of all the pigment in the adult, so that the adult of one species has been described by Creplin as "albi- dus" (Jagerskiold, 1891 :4). In some species of Allocreadiidae {Crepidostomum farionis O. F. M. and C. cornutum (Osborn)), pigment eye-spots are found in the adult. A still further stage of degeneracy is found in Cercaria racemosa (Fig. 100) and C. gracillima (Fig. 144), where the optic nerve is still present but the pigmentation is absent. In Cercaria gracillima, the representative of the furcocercariae, the ner- vous system is narrow, in correspondence with the attenuate condition of the animal. The posterior laterales are not found in the mature cercariae, altho the bud is present in the germ ball (Fig. 151). One is struck by the significant resemblance of the main nerve complex of this cercaria and that of Schistosoma haematobium, described in detail by Looss (1895). The three pairs of anterior trunks are readily made out, altho, in addition, a prominent dorsolateralis is found (Fig. 150). The posterior dorsalis arises from the dorsal side of the ganglion cell mass and proceeds caudad to the region of the acetabulum, where it fuses with the ventral trunk. A prominent subesophageal commissure and a small pharyngealis are present. The fundamental resemblance between the system described for this cercaria and that for the schistosome adult seems to the writer to be sufficient morphological evidence for the correlation of these apharyngeal furcocercariae with the Schistosomatidae. A study of the nervous system of the Holostomata has been made of Cer- caria ptychocheilus, based on both toto mounts and sections (Fig. 53). No adequate idea of the nervous system of this group can be secured from the meager data of Brandes (1891) and Thoss (1897). The dorsal commissure is 55] LIFE HISTORY OF TREMATODES— FAUST 55 indistinct and thoroly fused with the ganghon masses. The latter are wide, with a construction in each in the region of the origin of the lateral trunks. The trunks figured by Thoss are probably the ventrales, since they supply the main innervation of the animal. The anterior ventralis arises along with the posterior ventraHs just anterior to the latter. The anterior trunk soon divides. The major portion runs around the oral sucker, while the external branch is traceable anterolaterad. The anterior lateralis is represented by a blunt stock just outside the pharynx. It rims cephalad but soon ends in two delicate branches. There is no posterior dorsal of posterior lateral. The posterior ventral is stout and thick. It gives off one prominent branch ex- ternally soon after it reaches its most external position. At regular intervals it gives off branches internally which have the indication of rudiments of commissures. These transverse trunks just anterior and posterior to the acetabulum are still well developed; they are similar to those described for the distome. Contrary to the opinion of Looss (1894:245, 246), the writer has found without exception that the general trematode nerve anatomy can be traced from the early germ balls up thru various stages of growth, and that the cercaria shows not only the potentialities of the adult system, but actually the details of this system. Moreover, the study of various groups of cer- cariae has demonstrated that the fundamental deviations and modifications from type are recognizable in the mature cercaria. Thus this study has shown that the nervous system of the cercaria is constant for the group to which it belongs, and is a definite basis for the natural classification of the groups. In contrast to the highly developed nervous system found in the cercaria is that of the parthenita. In the sporocyst no definite nerve complex is found, altho Looss (1892) has observed nerve elements in miracidia of Amphistomum subdavatum. In the redia, however, with the continued functioning of the highly muscular pharynx, there is a nerve complex practically embracing the entire anterior portion of the gut (Fig, 125). Viewed from the dorsal, ventral, or lateral aspect, the system in surface view appears as an H. It is resolvable into four anterior trunks, four posterior trunks, and a ring commissure. On the dorsal side are two swellings, the rudiments of the cerebral ganglion masses of the cercaria. The nerve cells of the system are very prominent. They are usually bipolar or multipolar (Fig. 126), but, as might be expected, the more superficial ones are more often the multipolar cells. This redia nervous system constitutes a very primitive type, in which the nerve cells are much more frequently diffuse and more discrete than in the systems in the cercariae. It is probable that the pharynx is responsible for keeping the system from total degeneration. The size, number, and location of the ganglion cells vary according to indi- vidual species of cercariae. They may be situated within the ganghon centers, as in Cercaria micropharynx (Fig. 97) and C. glandulosa (Figs. 69, 70); they 56 ILUKOIS BIOLOGICAL MONOGRAPHS {56 may be scattered around the ganglia altho not imbedded in the fibers. In the redia of C. trisolenata the fibers are less conspicuous than the ganglion cells. Species closely related may have ceUs of different numbers and different sizes. In C. micro pharynx there are always just two ganghon cells, imbedded in the fibers, just above the esophagus. Their nuclei are large, pyriform, and usually containing conspicuous refractory nucleoli. They measure 5.5^i to 6ju in short diameter by 8.5^ to 9/i in long diameter. The nucleoli are about 2/i in diameter. Cercaria glandulosa presents a case where there is a definite number of minute ganghon cells within the ganghon masses. There are fifteen cells in each of the two masses. The cell walls are not well defined, but the nuclei are readily distinguished. They measure 1/x to 1.5/x in short diameter by 1.5m to 2/i in long diameter. The ganghon cells of C. pellucida are numerous; it has not been ascertained whether they are constant in ntmi- ber. They are subspherical at times, but are usually multipolar. The entire cell averages 3.Zti by 6n while the nuclei measure Iju to \.6n. The ceUs of the redia of C. trisolenata are usually multipolar in the region of the epidermis. They range from 6n to 22/i in diameter. The nuclei are inconstant in size, varying from 2/i to 6/i in diameter. The nuclei of the ganghon cells of C. gracillima are so minute in the nerve complex in the germ balls (Fig. 151) that they are barely visible under 1,000 magnification. Yet these nuclei are definitely set off from the surrounding matrix. They measure about 0.4/* in diameter. In cell-studies of adult trematodes the nerve cells have been measured in many cases. The measurements range from 80/i (Lejtemd, 1881:41) in Gas- trodiscus polymastos to 6/x (Fischer, 1883:17) in Opisthotrema cochleare. The nuclei range from 12/x (Juel, 1889:41) in Hemiurus excisus to l.tfi'va. Opistho- trema cochleare (Fisher). A comparison of these measurements in adult trematodes with those for the cercariae, shows that the nuclei of the adult cercariae are as large as those of the adult trematode. It is evident, however, that the cells are much smaller in the cercariae. Ageing of these cells consists, then, in the growth of the cytoplasm rather than an increase in size of the nucleus. S7J LIFE HISTORY OF T REM ATODES— FAUST 57 DESCRIPTION OF THE TREMATODES INFECTING MOLLUSKS OF THE BITTER ROOT VALLEY INTRODUCTION On account of the biological isolation of the Bitter Root Valley, it is little wonder that it contributes new species of trematodes. The fourteen species of trematodes found in the valley are not thot to comprise the entire trematode fauna of the region, but are the representative species for the year and season when the study was made. Of the fourteen species found in the Bitter Root River, two are larval Monostomata, two are Holostomata, and the remaining ten are Distomata. In addition to these, a larval holostome, Tetracotyle pipientis nov. spec, from the vicinity of Chicago, Illinois, is included in the study for the sake of comparison. Previous to the writers' preliminary report (Faust 1917) the following larval trematodes have been described for North America. Monostomata Distomata Cercaria hyalocatida Haldemann 1842 Cercaria polyadena Cort 1914 Glenocercaria liicania Leidy 1877 Cercaria hemilophura Cort 1914 Cercaria urbanensis Cort 1914 Cercaria trigonura Cort 1914 Amphistomata Cercaria trivohis Cort 1914 Cercaria inhabilis Cort 1914 Cercaria rubra Cort 1914 Cercaria diastropha Cort 1914 Cercaria douthitti Cort 1914 Cercaria gorgonocephala Ward 1916 Cercaria wrightii Ward 1916 Distomata Cercaria anchoroides Ward 1916 Cercaria agilis Leidy 1858 Cercaria marcianae La Rue 1917 Rhopalocerca tardigrada Leidy 1858 (Really a Distomulum) Gymnocephala ascoidea Leidy 1877 Cercaria vergrandis La Rue 1917 Cercaria platyura Leidy 1890 (Really a Distomulum) . Cercaria reflexae Cort 1914 Holostomata Cercaria megalura Cort 1914 Diplostomulum cuticula (v. Nordmann 1832) Cercaria leptacantha Cort 1914 Diplostomulum grande (Diesing 1850) Cercaria caryi Cort 1914 Diplostomulum volvens (v. Nordmann 1832) Cercaria isocotylea Cort 1914 Tetracotyle typica (Diesing 1858) Cercaria brevicaeca Cort 1914 Diplostomulum parmdum (Stafford 1904) Cercariaetim Cercariaeum helicis (Leidy 1847) Later recorded by Leidy as C. vagans (1850). In addition, there is the doubtful form, Cercaria bilineata Haldemann 1840. According to Stiles and Hassall (1908:157), Leidy is credited with the record of a species, Diplostomulum rhachiaeum (Henle). Investigation of the literature shows this to be an error, owing to the confusion of the names Leidy and Leydig. Fr. Leydig described the species D. rhachiaeum for Europe in 1853 (Leydig, 1853:383). Of the thirty-two forms listed, it is doubtful if any except those described by Cort (1914), Ward (1916) and LaRue (1917) could be recognized by their descriptions, since in the majority of cases the data are so indefinite as to leave the systematist a wide range of choice in determining the species. An excellent 58 ILUNOIS BIOLOGICAL MONOGRAPHS [58 example of this valueless type of description is afforded in the form Diplosto- mulum cuticula (von Nordmann 1832), reported by four American investigators from various localities east of the Rocky Moimtains. The descriptions include larvae encysted with pigment and without it, some specimens found subder- mally, others taken from the peritoneum of the body cavity, all secured from a great variety of teleost fishes. In none of the descriptions is there mention of the course of the excretory system or of the genital cell masses, both of which are essential to the exact determination of the species. It seems reasonably certain that a careful revision of these forms described as Diplostomulum cuticula (von Nordmann) would result in the discovery of several new species of Diplostomulvun. The species of cercariae and parthenitae described in this section of the paper have been studied with special reference to the excretory, genital, and nervous systems. MONOSTOMATA Cercaria pellucida Faust 1917 This larval trematode is a muscular cercaria, characterized by heavy anterior pigmentation on the dorsal surface, centered around three foci, the paired lateral eye-spots and the median eye. It is a member of the trioculate group of the Monostomata. The pigmentation tends to spread caudad from the pigment center along six Hues of growth, two dorsal, two lateral and two ventral. These lines of pigment have been shown (p. 53) to be the superficial index of the underlying nerve trunks. The worm is characterized by 1) a transparent body, 2) a circuit of refractory granules that marks the excretory system, 3) a small oral sucker, and 4) large longitudinal muscle bimdles of the tail. Cercaria pellucida was obtained from Lymnaea proxima Lea in the Bitter Root River in the vicinity of Corvallis, Montana, and from Physa gyrina Say near Buckhouse Bridge. The snails were examined in October, 1916. Lymnaea proxima contained a heavy infection with this species, along with a lesser infection with the monostome cercaria, C. konadensis, and a distome larva, C. diaphana. Physa was heavily infected with an echinostome, C. trisolenata, and contained only a hght infection with the monostome. In all cases the infected organs were the Uver ceca. The mature C. pellucida has an average measurement of 0.4 mm. to 0.7 mm. in length and 0.18 mm. to 0.2 mm. in width. The tail is about 0.5 mm. long and has a diameter of 0.07 mm. at the base. Most usually the animal has an eUiptical constricted outline, such as is shown in figiu-e 4, but when relaxed it assumes the elongate-ovoid or spatulate condition, shown in figures 1 to 3. The parthenita is a large conspicuous redia, measuring 2.2 mm. by 0.5 mm. (Fig. 6). Within the redia is a large rhabdocoel gut extending almost the entire length of the animal and measuring 0.3 mm. in cross section. The gut empties anteriad thru a muscular bulbus 15m in length and 12/x in cross sec- 591 LIFE HISTOR Y OF TREMA TODES—FA UST 59 tion. It is spinose internally (Fig. 20). In the prepharynx region is a unique piercing organ (Fig. 17), probably of ectodermal origin. It is four-lobed and is covered with spines. A rythmic eversion of the organ against the host tissue and redrawal within the pharynx region of the parthenita is a characteristic movement of the redia. Around the muscular pharynx is a ganglion mass consisting of a fibrous matrix and a network of ganglion cells. Behind the head region is a neck-like constriction, and behind the neck is a sacculate body. At the extreme posterior end is a large papilla. The redia is covered with a non-cellular basement membrane, and imbedded in this superficially in the form of minute tuberosities are the remains of the epidermal nuclei (Fig. 22). The walls of the redia are well-supplied with muscular layers, longitudinal and transverse, so that the parthenita is capable of extraordinary distension and contraction, altho it has no specific locomotor organs. The germ balls of the redia arise from the matured ova, derived from four cells localized at the posterior extremity of the parthenita. Altho the cells lying next to the wall around this quartet may be potentially germ cells, they take no part in the ordinary proliferation of germ cells (Fig. 22). From these cells arise the germ balls, thru cleavage into 2, 3 and 5 cells, after which cer- tain cells of the ball appear much smaller than the others and grow over the latter, giving rise to the gastrula by epiboly. The young germ balls usually lie en masse behind the gut, while the more advanced cercariae are crowded anteriorly. They appear strangely grotesque, with their pigment eyes and their snout-like bodies oscillating back and forth within the body wall of the par- thenita. Aside from the larger size of the body and the trioculate anterior end, Cercaria pellticida might be at first confused with Cercaria urhanensis Cort. While the size and eye-spots are sufficient to separate these two species, a more careful examination shows that there has not been a separation of two species at all, but more correctly two groups of species. The group of smaller species is binoculate and ranges around 0.3 mm. to 0.46 mm. in length by 0.1 mm. to 0,16 mm. in width, while the group of larger species is trioculate and averages around 0.5 mm. in length by 0.15 mm. to 0.2 mm. in width. Con- sequently from a description of external characters alone there is no means of separating Glenocercaria lucania Leidy from the Bitter Root species Cercaria pellucida. It is such a problem as this that has caused the writer to believe that there are characters more deeply seated in the larva that will readily set it off from others of the same group. Sufficient care in technic makes it possible to bring out very clearly and convincingly the genital organs of the Bitter Root species. Here are characters, constant both in the larva and the adult that readily differentiate these mon- ostome cercariae. These have been described in detail in the section devoted to morphology (p. 45) and need only to be summarized at this point. The median ovary just in front of the excretory bladder opens out thru a short duct at its left (Fig. 18), and after receiving the common vitelline duct, opens 60 ILLINOIS BIOLOGICAL MONOGRAPHS [60 anteriad into the uterus. This organ has an outlet just behind the median eye. It ends in a poorly developed vagina. No Laurer's canal has been definitely made out in the totos but there is evidence of such an organ in sec- tions. From the sides and sUghtly caudad to the ovary the closely massed testes open into filiform vasa efferentia which unite anterior to the ovary to form the vas deferens. This canal is directed forward parallel to the uterus, ending in a bulbous cirrus pouch just to the left of the vagina. The three paired outer vitelline follicular masses and the five paired iimer masses occupy a dorsal position. They are irregular in contour (Fig. 4), with aciculate margins, and are finely granular with close massing of the granules. Inconspicuous com- mon viteUine ducts connect the vitellaria with the ootype just dorsal to the ovary. The excretory trunks are similar to those of the entire group of monostomes. The bladder is quite small, 48/i in section, moderately muscular, superficially triangular, with the excretory pore posterior. The excretory tube in the tail is vesicular at the base and narrows down distad (Fig. 4). The tubes of the tnmk are crowded with large excretory granules. The digestive system is t3T)ically triclad, with ceca extending to the sub- distal extremity. They are filled with a jell, and are crowded with granules imbedded in the jell. No pharynx has been observed. The oral sucker is directed ventrad. It is small but powerful. The parenchyma is filled with cystogenous granules, included in one-celled cystogenous glands, probably of mesodermal origin (Fig. 14). Between the cystogenous cells are angular parenchyma cells, more commonly known as vesicular cells (Blasenzellen), with processes extending to the integiunent and possibly functioning in the capacity of secretory ducts for the basement mem- brane. The locomotor organs at the posterior angles of the tnmk are neither spicu- late nor spinose. They possess no cement glands. The tail has no central pair of gland elements such as axe found in binoculate cercariae of the mono- stome group. However, the ordinarj' parenchyma cells of the tail of C. pelltt- cida are remarkably large and vesicular and suggest a glandular function (Fig. 19.). Large, isolated bands of transverse muscle fibers are present thruout the body just within the basement membrane. Longitudinal muscles are not so large in the tnmk as are the transverse series, but constitute the important muscle system of the tail. The transverse muscles of the tail frequently give a moniliform appearance to that organ, such as is described by Leidy (1877) for Glenocercaria Iticania. The nervous system of C. pellucida (Fig. 23) varies from the distome nervous system only in its relation to pigmentation and the eye-spots. There are six anterior tnmks and six posterior trunks arising from a paired brain center. They constitute the dorsal, lateral and ventral nerve lines. These trunks are carefully followed by the melanoidin pigment fraction. The eye-spots receive 61] LIFE HISTORY OF TREMATODES—FAUST 61 innervation from the dorsal trunks; the paired eyes are innervated from the posterior trunks and the median eye from the fused branch of the anterior dorsales. The optic nerve runs forward from its origin in the dorsalis and enters the pigment cup from above, ending in a sensory cell (Fig. 24). The general anatomy and histology of this eye-spot is similar to that described for all Turbellaria and Monogenea. However, no previous account has been found for the structure of the eye-spot of the Digenea showing its relation to the central nervous system. Locomotion is brought about thru a cooperation of the body musculature together with the special functioning of the oral sucker and the posterior loco- motor pockets. The tail serves as a swimming organ, with a peculiarly rapid and nervous lashing. Encystment occurs as a fmal step in the larval stage of the life-history of the hermaphroditic generation, in preparation for entering the definitive host. The process is rapid and the mucoid cyst is secreted by the cystogenous glands before the tail has been thrown off. This organ is freed from the cyst by the violent wriggling which it produces. The cyst is spherical; it encloses the now quiescent larva. The outer portion of the cyst is an opaque mucoid, which gives the cyst an appearance of a white grain, about the size of a pin-head. The larva now waits transfer to the definitive host. Cer carta konadensis Faust 1917 Cercaria konadensis is a species of monostome cercaria of the binoculate type. The species is more graceful than C. pellucida. Its bodily contour is most usually spa tula te, while the long tail reaches far behind. The small amount of pigmentation around the two eye-spots and the less usual pigmenta- tion along the nerve trunks caudad serve to indicate the superficial differences between the binoculate group to which this form belongs and the trioculate group. Cercaria konadensis was found in Lymnaea proxima Lea, collected from the Bitter Root River at Corvallis Montana in October 1916. It occurred as an infection along with the larger species, C pellucida. Of the snails examined, 31.3 per cent were infected with this cercaria in the connective tissue be- tween the liver ceca. The cercaria measures 0.4 mm. to 0.46 mm. in length and has a bodily width of 0.1 mm. to 0.16 mm. (Fig. 25). The tail is of equal length under conditions of relaxation, but may be extended so as to*exceed by far the bodily length. At its base it has a transverse diameter of 30/x to 40jU. The posterior locomotor organs are not so conspicuously lateral as those of C. pellucida (Fig. 4). Considered together with the younger stage of C. pellucida (Fig, 12), these pockets suggest an origin from the caudal pockets found in certain distome cercariae. Unlike those of C. pellucida, the posterior locomotor pockets of C. konadensis are provided with about ten gland cells surrounding the lumen, cells probably of a secretory nature (Fig. 21). 62 ILLINOIS BIOLOGICAL MONOGRAPHS [62 The parthenita (Fig, 26) is a relatively small, elongate redia, 1.7 mm. in length and 0.35 mm. in transverse section near the middle. It is attenuately obtruncate, with the posterior end sloping down to a blunt point. The pharynx is muscular but small, 60)u in cross section, and aspinose internally (Fig. 31). The rhabdocoel gut extends posteriad about three-fifths the body length. The posterior end is filled with cells, composed of a central rachis with apex directed posteriad, and an outer cell complex of goblet cells (Fig. 30). The central rachis comprises the germinal epitheUum, the proliferating region of which is situated sub terminally. From this epithelial mass the matured parthenogenetic eggs are proliferated forw'ard so that the germ balls come to lie in the lumen posterior to the gut. Similarly to those in C. pdlucida, only the maturing cercariae come to lie around the gut. The excretory system of C. konadensis consists of the circuitous trunk system, opening posteriorly into a non-muscular vesicular bladder. This vesicle measures 16)Lt to 17/i in width and 14/i to 15^ along the longitudinal axis of the cercaria. The excretory pore is dorsal, opening from the middle of the bladder (Fig. 29). The digestive system is of the usual triclad tjpe, with no distinct pharyn- geal region. The genital organs are notocotyhd in character, but different in several fea- tures from those of C. pellucida. The ovary (Fig. 28) is skull-cap shaped, with a distinct Laurer's canal. A short oviduct leads into the ootype. The uterus, emerging from the ootype, runs cephalad, ending in a swollen vagina some distance behind the line joining the paired eye-spots. The vitellaria consist of a double series of five inner and three outer follicular masses. The indi- vidual glands are very diffuse and dendritic. The testes are small, lateral, and posterior to the ovary, with the vasa efferentia describing a broad crescent anteriad around the ovary and meeting in a common tube, the vas deferens, which runs forward to the left and parallel to the uterus. The vas deferens ends in a swollen cirrus pouch (Fig. 25). The nervous system corresponds to the monostome type described for C. pellucida, except that the dorsal trunk to the median pigment eye-spot is lacking. In the tail six paired groups of gland cells, derived from parenchyma, occupy places just lateral to the median canal of the excretory system, each group dove-tailing into the one next proximal. These caudal glands indicate a much closer kinship of this worm to Cercaria urbanensis than to C. pellucida. Encystment is brought about by the pouring out of the contents of the cystogenous cells and by subsequent decaudation. HOLOSTOMATA Cercaria flabelliformis Faust 1917 Cercaria flabelliformis is the first larval holostomid to be described in detail for North America. Leidy has listed Tetracotyle typica Diesing from 63] LIFE EISTOR Y OF TREMA TODES—FA UST 63 Lymnaea catascopium and Fkysa heterostropha (1890). Rettger (1897) has mentioned a larval tetracotyle in connection with a life-history study, but he has failed to identify the species. Cercaria flabelliformis was found in three collections of Physa gyrina Say, taken from the Bitter Root River in the vicinity of Corvallis, Montana, in October 1916. Practically every snail from these collections bore evidence of infection with the parthenita of this species, altho only 14.7 per cent of the snails examined contained the tetracotyle. The mature cercaria has a length of 0.48 mm. to 0.56 mm., and a width of 0.44 mm. It is about 0.2 mm. thick. While the anterior end is not clearly set oflf from the posterior end as is usual in holostomids, it does have the suctorial cup which includes all the ventral suctorial apparatus, including among the rest the lateral suctorial grooves. In the young larva these lateral organs are discoidal (Fig. 41); in the mature tetracotyle they have become modified into lateral lappets (Fig. 40). The larva was found maturing within the redia, free in the liver interstices, and encysted in the Hver tissues. It was seldom found free in the tissues. The parthenita (Fig. 42) is a redia which measures 0.5 mm. in length by 0.052 nun. in transverse section. The head is set off from the trunk by a collar prominence, while in the posterior third of the body are found the "walking feet, " which protrude ventrolaterad to support the redia. The posterior end of the body is produced into a large knob, in which are parenchyma and germinal epithelium ceUs. At the oral end is a wide muscular organ. It is not clear whether it is a pharynx or an oral sucker. It is about 40/i in trans- section and surrounds the fore-end of a gut 0.18 mm. long. On the ventral side are two groups of saHvary glands, six cells to each group, opening into the anterior region of the gut thru a common duct for each group (Fig. 43). Around the anterior end of the gut, just behind the muscular organ, is a nerve complex (Fig. 42), differentiated into two ganghon masses on the dorsal side, four nerve trunks, and a circimiintestinal commissure. A birth-pore is here ventral and shghtly sinistral. The wall of the parthenita is heavily covered with an integimient of non-cellular material, beneath which are muscle and parenchyma elements. Running thru the parenchyma is a com- plex diamond-pattern excretory system. The germinal epithehum is localized at the posterior end of the redia. It offers an unusually fine opportunity for study of the maturation of the ova. The detailed description of this maturation is found in the section on morpho- logy (p. 16). The germ balls may differentiate into a second generation of rediae and cer- cariae at the same time. These larvae are about equal in size as they develop, but the cercariae differentiate much more rapidly than do the rediae so that the two are readily distinguished. Usually only three or four cercariae are found developing at one time in the redia, along with many daughter redia. This fact seems to indicate that the animals have come to depend largely on parthenogenetic propagation. The cercariae escape thru the birth-pore and 64 ILLINOIS BIOLOGICAL MONOGRAPHS [64 soon encyst in the free tissue of the host. The second generation redia is aheady producing germ balls before it comes to take up a free existence out- side the first generation redia. The internal systems of organs of Cercaria flabelliformis are of considerable interest. However, since they are described in detail in the respective sections in the morphological division of this paper (pp. 37, 45, 54) they will not be treated here. Valuable data on holostomid anatomy are obtained by a comparison of Cercaria flabelliformis with the following species: Tetracotyle pipientis nov. spec. This species of larval trematode was found in March 1917 in the mesentery and pericardium of a large number of Rana pipiens collected in the vicinity of Chicago, Illinois. All of the frogs were more or less infected with this holostome. The infection consisted of creamy oval yellow cysts, either single or in grape-like clumps. Each cyst consisted of many lamellae, and innermost, a tough cyst membrane. The inner membrane stains a deep brown with iodine in 70 per cent ethyl alcohol. The gross measurement of the cyst ranges from 0.5 mm. to 0.76 mm. in lesser diameter and 0.7 mm. to 1.0 mm. in greater diameter, while the inner membrane is about 0.3 mm. by 0.5 mm. Within the inner membrane is the larva, tightly coiled at one end of the cavity, while the remainder of the cyst, often two-thirds of the volume, is filled with accum- ulations of large excretory granules. Some of these granules have fused to form single clumps as large as the larva WTien the lamellae and cyst membrane are teased open and the larva is allowed to work its way out, the body becomes expanded and flattened. It then measures 0.5 mm. in length by 0.37 mm. in trans-section (Fig. 47). The oral sucker is 75)U in diameter. It lies in an anterior cone of the body. Antero- lateral prominences and the blunt posterior portion of the body give a lyrate outline to the worm. The primitive genital pore, 80;u in diameter, lies in a plane where the anterior and posterior portions of the body join, just within the suctorial pocket. The free ventral wall of this pocket is often folded backward so that it fits down snugly against the body. At other times it bulges out so that the pocket cavity is a large ovoid atrium. The acetabulum is represented by a single lappet situated behind the primitive genital pore. The non-muscular accessory suctorial grooves consist of long narrow slits, directed obliquely inward toward the acetabulum. The entire worm is covered with minute anterior and posterior spines, equally prominent. The primitive genital pore is crowned with a ring of fused spines. The lateral suctorial organs are surrounded by a band of discrete spines imbedded in the tissues. The worms examined were all filled with excretory granules. A careful study of the larva showed the main course of the excretory trunks to appear as shown in figure 48. The median posterior excretory pore, sUghtly dorsal, conmiunicates with the bladder which merges imperceptibly with the paired 65] LIFE HISTORY OF TREMA TODES—FA UST 65 lateral trunks. These tubes lie just within the margins of the larva and unite with one another in a large transverse vessel at the anterior end of the body, so that a complete circuit is formed. If a rent is produced in the body near the oral sucker, it is customary for the excretory granules to be poured out there rather than thru the natural channel. A tube from the lateral trunks crosses thru the ventral pocket wall at its anterior end. Tributary tubules, bisymmetrically arranged, empty into the main trunks, mostly at the anterior and posterior margins of the body. The digestive tract is simple and inconspicuous. A small swelling within the oral sucker marks the pharynx, just behind which is the esophagus. The ceca barely clasp the anterior margin of the primitive genital pore. The genital organs are readily recognized as holostome in type (Fig. 47). They open posteriad. A small spherical ovary lies median. Dorsal to this is the ootype, into which come the short oviduct and the transverse vitelline ducts. The vitellaria are diffuse bands of large follicles extending from the anterior face of the acetabulum to the posterior margin of the genital pouch. They lie strictly ventral. Two large oval testes lie to the sides of the ovary, the one (ti) slightly anterior to the other (t,). They have individual ducts (efferent) which reach the genital pouch and fuse into a common vas deferens just before entering the genital pouch. This organ is muscular, oval in con- tour, with the transverse diameter longer than the longitudinal. A survey of the literature shows that only one tetracotyle has been re- ported for Amphibia, Tetracotyle crystallina (Rud.), from the mesentery cysts in Rana temporaria, R. esculanta, Bufo igneus, B. viridis, and Vipera berus (Rudolphi, 1819:380-382). The formation of the cysts is not clearly de- scribed, but the large size of the Europen tetracotyle, together with its oval contour, aspinose body and oval accessory sucking discs, clearly separates it from Tetracotyle pipientis. The new species conforms much more to the type represented by T. cohibri v. Linstow, but differs from it in the relative sizes of the oral and ventral suckers, and the possession of small spines all over the body instead of a few broad spines (Linstow, 1877:192; Fig. 22). While the excretory system is one of the best systems of organs to use in systematic work with trematode larvae, in the absence of such data for other tetracotyles. described, the comparative data actually afforded are sufficient in this case to justify the establishment of Tetracotyle pipientis as a distinct species. Observations on the anatomy of Tetracotyle pipientis present an oppor- tunity for comparison with Cercaria flabelliformis, the parasite of the Bitter Root moUusk, Physa gyrina. The two larvae are about equal in length, but C. flabelliformis is consider- ably the wider. The widest region in T. pipientis is in the anterior region of the body; the widest portion of C . flabelliformis is in the middle of the body. The suctorial pocket in the former species has grown over the ventral sur- face so that a true pocket is formed with the opening anterior; in the latter 66 ILUNOIS BIOLOGICAL MONOGRAPHS [66 species the suctorial pocket is hemispherical with the opening ventral. The lateral accessory suctorial grooves in T. pipientis are non-muscular oblique slits; in C. jlabelliformis they are at first oval depressions which are modified later into a pair of lateral lappets. The primitive genital pore in C. fiabelli- formis is 0.05 mm. in diameter; in T. pipientis it is 0.08 mm. wide, with a crown of heavy spines. The homologies between the lateral excretory trunks of the two species are apparent, altho the median transverse trunk is much farther anterior in T. pipientis than in C. Jlabelliformis. The tributar}' tubules are entirely different in the two species. The digestive ceca of the Bitter Root species conform to the family type in extending well into the posterior part of the body; those of T. pipientis are short and rudimentary. The geni- tal organs of the two species occupy the same relative position, altho individual variations in size and shape of organs are evident. In concluding the study of the tetracotyle larvae, emphasis must be placed on the maturation of the parthenogenetic ova, which shows that these larvae do not develop in miracidia, without the intercalation of parthenitae as Brandes (1891:572) and Fantham (1916:224) beUeve. This fact, previously recorded by the writer (1917), makes the morphological evidence complete in support of the view of true alternations of hermaphroditic and partheno- genetic generations among Holostomata. Cer carta ptychocJieUus Faust 1917 This form, really a Diplostomulum, is elongate ovate in outline, with dorso- ventral flattening, sHght ventral concavity, and a more or less distinct sepa- ration of body into anterior and posterior portions. In addition, the group to which this worm belongs lacks the lateral auxiHary sucking grooves which are characteristic of the tetracotyle forms. Several species of Diplosto- muliun have been weU described and their excretory system beautifully traced by von Nordmann (1832). These include the species Z>. volvens,D.cuticula, D. clavaium, and D. breoicaudaium. Of the forms found in North America there have been recorded D. cuticula, D. volvens, and D. grande of the Old World species, and D. parvulum (Stafford), new to North x\merica. However, as has been previously suggested, none of these American records give suf- ficient data to distinguish accurately the species. The general outline of the body of Cercaria ptychocheilus is such as to dis- tinguish it readily from the described species. Broadly oblong-ovoid in contour, with the anterior half laminate and the posterior portion fleshy, this cercaria might at first be confused with distome cercariae. Such a con- fusion is caused, further, by the abbreviated appendiculate portion of the larva, which, on extension into a caudal cone, may reach one-third of the body length, but on contraction barely protrudes behind the anterior part of the body. The concavity of the anterior part is found only in the fleshy region behind the acetabulum. Here in this area is foimd the muscular complex comparable to the cup-shaped suctorial apparatus of the tetracotyle. 67] LIFE HISTOR Y OF TREMA TODES—FA UST 67 The Diplostomulum (Fig. 49) measures 0.48 mm. to 0.63 mm, in length by 0.17 mm. to 0.37 mm. in width, and about 30^ thick in the fleshly portion of the body. The oral sucker is small but powerful, and is directed strictly anteriad. Behind this oral region the esophagus is enlarged into the pharynx, about 40/x in section. Behind the pharynx is an equal portion of the esopha- gus which is non-muscular, posterior to which the ceca rise, spreading out into a broad furculum. The acetabulum is large and circular; it is situated somewhat posterior to the middle of the body. At times of extreme contraction the acetabulum becomes narrowed antero-posteriorly, with a transverse wrinkling. This disc measures 70ju in diameter. The primitive genital pore, situated just in front of the acetabulum, has lost its connection with the genital system and has become modified into a muscular sucking disc. The excretory, genital, and nervous systems have been treated on pages 37, 45, 54, as types for the hemistome larva. A comparison of these data with V. Nordmann's observations on Diplostomulum cuticula, D. volvens, and D. clavatum, and with the work of Blanchard (1847) on Hemistomum alatum (Goeze) shows the fundamental conformities and differences of the excre- tory systems of the group. However, the nervous system (Fig. 53) is worked out thoroly in this paper for the first time in the Hemistomidae. The genitalia bear a fundamental resemblance to those of the adult species, as described by Brandes (1891), but differ in size, shape and position of the respective organs. This difference may be accounted for in part by the immaturity of some of the organs, but there are undoubtedly specific differences, such as the lamellae of muscular nature in the genital pouch and the glandular cells emptying into the pouch. The larva Cercaria ptychocheilus was taken from mesentery cysts of Pty- chocheilus oregonensis Richardson, caught in the Bitter Root River in April 1915 in the vicinity of Stevensville, and Carlton, Montana. Thousands of cysts were found. The cysts are much larger than the larvae (Figs. 50, 51) and are filled with a limpid milky fluid which bathes the larva and serves as a liquid cushion. The cyst is oblong, and flattened. It is composed of a thin, tough membrane, and it is attached to the mesentery by a discoid annulus in the middle of one of the flattened sides. Within the cyst the worm works around and grows, so that it comes to fill the cyst in later life. At frequent intervals there is extruded from the excretory bladder a considerable quantity of granules which pile up at the posterior end of the larva within the cyst, but are soon dissolved and absorbed by the fluid medium. The encysted animal when placed in a normal saline solution soon increases its activity and bursts thru the cyst. This rent usually occurs at one end of the membrane. The larva then crawls out with a "measuring worm move- ment. " After several hours of activity it settles down on the bottom of the container and remains quiescent, altho sUght mechanical disturbances activate 68 ILLINOIS BIOLOGICAL MONOGRAPHS [68 it again. In a modified Ringer's solution ninety per cent of these larvae were kept alive for forty-eight hours. It seems probable that Cercaria ptychocheilus is in an intercalated host. DISTOMATA Xiphidiocercariae (St}'let Larvae) The xiphidiocercariae are grouped together because of their possession in common of a larA^l stylet. The writer beHeves that the features of the geni- tal and excretory systems of the group are more fundamental characters which will hold the members of the group together. Cercaria crenata Faust 1917 Cercaria crenata is a delicate larva, with an ovate bodily outline and a short lanceolate tail (Fig. 55). The body measures 0.25 mm. in length by 0.13 mm. in width, and the tail, 0.15 mm. to 0.16 ram. in length by lOjx to 30/1 at the base. The entire body except the tail is covered with minute hair- like spines. A large median spine, the stylet organ (Figs. 56, 57) hes in the dorsal wall of the oral hood. This organ is about SO/z long by 5/x in width at its base. It has the general shape of a quill pen, with reinforcements at its base and also in the distal portion toward the acute point. The distal third of the stylet is bent ventrad about 20 degrees. There are two prominences in the anterior portion of this organ, one where the shaft joins the quill and a less prominent one-half way between this position and the quill point. The oral sucker is relatively large, 20^ in diameter, while the acetabulum, situated three-fifths the way from the anterior end, measures just half that diameter. The tail is inserted in the posterior caudal pocket which has no spinous projections. Cercaria crenata was found in large numbers in 13.6 per cent of Lymnaea proxima Lea, taken from the springs at Fort Missoula, Montana, in October 1916. It occurs in oval sporocyst sacs, 0.5 mm. in length and 0.35 mm. in diameter. At one end the germinal epithelium, is localized and from this end the ova are proliferated. Only cercariae have been found to develop within the sporocysts. When the cercaria is mature its breaks thru the wall of the sporocyst and swims thru the surrounding medium. The tail is retained for a consider- able time, and encystment is slow. This seems to indicate a considerable period of free-swimming Hfe. The internal structure of Cercaria crenata is such as to distinguish it readi- ly from the other stylet cercariae. The excretory system is characterized pos- teriorly by a subspherical vesicle, deeply crenate. It measures 20/i long and 30/i wide. Anterior to the bladder a bicornuate trunk empties into the ves- icle thru a common median tube. The horns of the U are widely separated. At the place where each main lateral turns forward there is given off a small dendritic tubule, directed posteriad. Some distance ahead of the acetabulum 69] LIFE HISTOR Y OF TREMA TODES—FA UST 69 the main lateral trunk divides into inner and outer tubes, each of which has a number of branches and capillaries. The main tube of the tail is median, with no prominent tubules. The digestive system consists of an esophagus provided with a pharynx for most of its way, and, behind the pharynx, a typical gut extending to the posterior plane of the acetabulum. The salivary-mucin glands in C. crenata are of a unique type. An outer series of eight small vesicular cells, with a common duct system into the oral pocket, corresponds to the usual salivary-mucin gland system of cercariae. These glands are readily made out in the living worm. An inner series of five cells, two of which are just behind the pharynx and three behind the ace- tabulum, empty thru a common duct system into the oral pocket. This series is not seen in the living larva, but in stained specimens the cells show small vesicular nuclei with deeply staining cytoplasm and numerous chromo- philic granules. This inner series probably consists of a type of salivary gland different histologically and suggests a correspondingly different function. The genital cell masses are prominent and are well differentiated early in development. Their structure and position are indicated in figure 59. The ovary lies posterior to the acetabulum and median whereas Laurer's canal lies anterior and to the left. The uterus is characterized by a double coil, which ends in a moderate sized vagina, just anterior to the acetabulum. The vitellaria are limited to three cords which lie in a transverse plane just posterior to the ovary. The large flask-shaped testes lie behind the ovary. This genital system suggests the Plagiorchiine arrangement. The distribution of vitellaria is similar to that described by Poirier for Plagiorchis sauromates (1886, pi. 2). Cercaria glandulosa Faust 1917 A stylet cercaria characterized by a multiplicity of glands has received the name of Cercaria glandulosa. It is somewhat larger than C. crenata, is more oblong-ovate, and is a much more active larva (Fig. 60). The body measures 0.45 mm. in length and 0.2 mm. in width. The tail is slightly shorter than the body, 0.35 mm. in length, by 50/i to 60/i in section at the base. The tail is set within the caudal pocket. This pocket is provided with a pair of locomotor grooves, in which are set a number of stiff spines. Below the insertion of the tail is a small lappet (Fig. 63), provided with three spines directed posteriad. A mucoid secretion is present in the sinuses of the pocket, lateral to the base of the tail. The stylet organ measures 39yii in length by 5m in width at the base of the shank. It is reinforced all thru, but especially at the base of the shank, and thruout the quill. The point of the stylet is blunt. The stylet, as well as the entire body, is very delicate, and is shattered by the slightest pressure of the cover slip. The oral sucker is directed downward; it measures 86^ in diameter, while the acetabulum, in the middle of the ventral side, is smaller, with a diameter of 66//. 70 ILUNOIS BIOLOGICAL MONOGRAPHS 170 The cercaria was found in the liver tissues of Physa gyrina Say from the Bitter Root River in the xdcinity of Hamilton, Montana, in October 1916. Forty per cent of the physas examined were infected with the parasite. The cercaria develops within a very simple sporocyst, which has a length of 0.34 mm. and a width of 0.17 mm. (Fig. 67). The wall of the sporocyst is delicate, consisting of a single layer of very thin epidermal ceUs, with no basement mem- brane and no muscular complement. The genital epithehum is localized at one end, and from this only a few cercariae are developed at any one time. The excretory system of Cercaria glandulosa presents some interesting features. The bladder is flattened, truncate, and subterminal instead of terminal. A narrow canal communicates with the excretory pore which is median posterior. The four angles of the bladder are muscular. When the bladder is emptied these corners lie close together, so that the cavity of the bladder is small. Then by the expansion of the bladder this organ is filled from the trunks (Figs. 64, 65). Two vesicular cornua empty into the bladder. Each cornu is directed laterad and sKghtly anteriad; it soon constricts to form the lateral tube. The common tube divides soon to form the posterior tubule and the anterior tube. The anterior vessel then divides in the region of the acetabulum to form a trifurcate system. Just behind the region of this division there is a small vesicular swelling where granules of the system accumulate. The excretory system in the tail consists of the common medi- an vessel and several tributaries. The digestive system is characterized by an abundance of glands, so that the entire tract is surrounded with gland cells. A small pharynx surrounds the esophagus near the anterior end of the tube. The esophagus extends to the preacetabular region, at which place it forks to form short furcae which barely clasp the anterior end of the acetabulum. Along this entire course there are many gland cells in clusters, especially abundant in the pharynx region. Their relation to the pharynx and nerve gangha is shown in figure 72. The individual gland ceU is ovate, with a short neck. The cytoplasm is chromophilous. There is no recognizable duct connection thru the myoblasts of the pharynx to the lumen. The nuclei of these cells are large and studded with granules. In addition to the grape-like clusters of gland cells surrounding the entire digestive tract there are right and left paired gland groups of the salivary- mucin type. They consist of nine large cells to each group, usually situated in the acetabular region, but capable of extension, so that they may He as far caudad as the bladder (Fig. 62). Figures 73 and 74 show sections passing thru the anterior tip of the excretory vesicle. In each of these a right and a left gland are visible. In these glands not only is the nucleus granular, but the cytoplasm is densely granular, the granules being assembled in little climips. Frequently (Fig. 73) there are vacuoles within the cytoplasm. 'i%^ The genital organs are represented by cell masses which show clearly the location of the mature organs, but as yet show little differentiation (Fig. 71] LIFE HISTORY OF TREMATODES— FAUST 71 66). Ovary, Laurer's canal, vagina, uterus — all are recognized in the midace- tabular region, with vitelline follicles extending from the oral aperture to the posterior end. They are divided into anterior and posterior portions. No testes are yet to be found. The genital organs as a whole seem to indicate Plagiorchid relationship. Conspicuous thruout the body are the large bundles of longitudinal muscle fibers. They are scattered thruout the parenchyma at the anterior end (Fig. 72), while they are much larger and more concentrated laterad in the region of the acetabulum. Still further caudad they become fewer and less conspicuous (Fig. 74). The nervous system has been described in detail on page 51. This cercaria lives a free-swimming existence for only a short time. When placed in a watch-glass in tap water, it soon drops its tail, preparatory to encystment. The tail is helpful in locomotion, yet after decaudation this species is more active and able to cover considerably more ground than most other species v/ith the aid of the tail. This movement is due in no small measure to the spines in the locomotor grooves of the caudal pockets. After moving about for a little while the cercaria settles down and pours out an abundance of shme within which it coils up and becomes quiescent until a transfer to the new host is effected. Cercaria diaphana Faust 1917 Cerceria diaphana is closely related to C glandulosa. When contracted, it is broadly ovate (Fig. 78), but on extension it assumes an elongate ovoid contour (Fig. 76). The measurement of the body when at rest is 0.2 mm. to 0.26 mm. in length by 0.1 mm. to 0.12 mm. in width. Under pressure of a cover slip the internal organs are beautifully worked out and the delicate mist of the parenchyma in which they are imbedded suggests the term "dia- phanous. " The tail is broadly lanceolate, 0.15 mm. in length by 0.04 mm. at the base. It is inserted into a caudal pocket provided with spinose locomotor pocket grooves. The spines are few in number (8 to 10) and well developed. They are directed meso-caudad. As in C. glandulosa the two sinuses of the caudal pocket are thickened by a mucoid lamination. The acetabulum is situated in the middle of the ventral side; it has a diameter of about 32/i. The larger and more powerful oral sucker has a diameter of 44/i. The stylet organ (Fig. 77) is a delicate but firm quill of 39/i length and Sn width at the base of the shank. It is entirely without any reinforcement in the region of the shank but has thin ventral plates at the junction of the shank and quill, while inserted in the quill point, directed posteriad, is a minute spine, 5/* long and 0.5^1 in diameter. Cercaria diaphana was found in the liver tissues of Lymnaea proxima in the Bitter Root River near CorvaUis in October 1916. The infection was heavy. The cercaria develops in an oblong sporocyst (Fig. 79), frequently drawn out or contorted at one end (Fig. 80). The unique feature of the 72 ILUNOIS BIOLOGICAL MONOGRAPHS [72 sporocyst is that the germinal epithelium is not localized; consequently germ balls may be derived from any portion of the body. Whether or not the germ cells arise parthenogenetically has yet to be determined. This type of germ ball production represents a structural simplicity previously not recorded for the sporocyst. The excretor\' system differs from that of other stylet cercariae mainly in the shape of the bladder and of the essential tubes. The bladder is small, hea\'ily muscular, flattened antero-posteriad. Leading out from it in a median plane is a non-muscular shank of some length, which opens into two cornua a considerable distance in front of the bladder. Caudad these cornua are vesicular, but further cephalad they become constricted into a system of tubules similar to those of C. glandulosa, w^hich nm thru the body to collect the excretor\' wastes. The digestive system consists of a long esophagus, with pharjTix at the anterior end, and a wide bifurcation somewhat anterior to the acetabulum. The entire digestive tract is very attenuate in outline. It is not supplied with glands along the furcae but has an even more abundant supply than C. glandulosa in the region of the pharynx (Fig. 76). Altho the pharynx itself measures only 15/x in cross section, the glandular area as a whole em- braces a sphere 65ju in diameter. The rest of the tract is free from gland cells of this nature. The saUvar\--mucin glands are situated in the upper outer reaches of the furcae. Each group consists of eight cells, relatively very small, granular, with a common duct system opening into the oral pocket. The genital organs are similar to those of C. glandulosa (Fig. 78). They differ from the genital cell masses of that form in the more limited vitellaria, and the more conspicuous Laurer's canal. This form is probably a Plagiorchid larva. Unlike C. glandulosa this cercaria is slow to drop its tail and much slower to encyst, in spite of the fact that there is an equally good pair of posterior locomotor pockets with spines and an equally good supply of c}'stogenous. material. We have here, then, e\'idence of a physiological adaptation to different conditions of the en\-ironment, where the structure of the two t}'pes would lead one to expect similar habits and reactions. Cercaria dendritica Faust 1917 Cercaria dendritica is a species of cercariae readily recognized by its obovate structure, large suckers, large muscular phar\'nx, and large muscular excre- tor\- vesicle. The body as a whole is heavily muscular. The tail is short and almost conical (Fig. 81). The body measures 0.33 mm. to 0.4 mm. in length by 0.13 mm. to 0.17 nmi. in wadth. The tail is about half the body length, 0.16 mm. and is 0.04 mm. wide at the base. It is inserted into a typi- cal caudal pocket, the whole ca\"ity of which is lined with stiff spines. The large oral and ventral suckers are nearh' equal in size. The former has a diameter of 62^ and the latter of 60;/. The stylet (Figs. 82, 83) is short and stout, heavily reinforced at the shank, with a flat deltoid quill. The quill 73] LIFE HISTORY OF TREMATODES— FAUST 73 is pointed at the tip. It is directed ventrad by about ten degrees more than the shank. The stylet has a length of 44/i and a breadth at the base of the shank of 14/x. Cercaria dendritica was secured from two collections of Lymnaea proxima taken from the chara sloughs at Fort Missoula, Montana, in October 1916. The infection was in the liver interstices. The parthenita (Figs. 87-89) is a well-developed sporocyst, with an attachment disc, but without any indica- tion of a digestive tract. It seems to approach a redia more nearly in its structure than any other described sporocyst. The sporocyst is muscular and heavily covered with integument. The parthenogenetic eggs develop from a germinal epithehum situated at the antipodal end from the disc. The stages of cleavage are clearly made out from the study of the germ cells pro- liferating from the germinal epithelium (Fig. 89). This layer is closely pressed against the epidermis. As the cells mature they increase in size. The increase continues thruout the cleavage, so that a three-cell stage is larger than a one-cell stage, and a morula is larger than a five-cell stage. This continued growth of the embryo is accounted for by the nourishing medium which bathes the sporocyst. This is a special case of nurture, where the growth stimulus is reacted to immediately. The germ ball attains a con- siderable size before it begins to differentiate, altho epiboly has occurred soon after the morula stage has been reached. The animal is mature before it breaks thru the wall of the sporocyst and swims out into the inter-cecal spaces. The larva has an interesting excretory system (Fig. 81). An immense spheroid bladder, somewhat crenate, opens dorso-posteriad thru a small pore. Anterior it receives the contents of two large muscular comua thru a common opening. These cornua extend laterad to the extreme margin of the animal. At the outside of each, at the margin of the worm, arise three tubes, one directed posteriad and two directed anteriad. The capillaries are dendritic. The caudal tube is a median canal without any prominent tubules. The alimentary system consists of a pharynx with muscular fibers developed early. It has a width of 30^ and a length in section of 36ijl. A short, attenuate esophagus opens posteriad into two vestigial furcae. Anterior and lateral to the acetabulum are the salivary-mucin glands, eight to each group. They are moderately large (Fig. 85), and empty thru common duct systems into the oral pocket. The conspicuous features of the genital system (Fig. 86) are the large swollen vagina, and the prominent Laurer's canal, the latter extending out on the left side of the acetabulum under its posterior margin. In the mid-area, just behind the acetabulum, are two small pyriform testes. The vitelline glands extend from the extreme anterior margin of the worm to the extreme posterior end; they are attenuate, sparsely branching serpentine chords, composed of a long anterior and a short posterior portion. The vitelline ducts run in from the postero-lateral regions to the ootype, which is just anterior to the testes. This type is suggestive of Plagiorchid relationships. 74 ILLINOIS BIOLOGICAL MONOGRAPHS [74 Soon after the cercaria is set free into the water, it drops its tail. Ahnost before the observer is aware it secretes a thin membrane from the abundance of cystogenous material contained in the large cyst cells which pack the paren- chyma of the worm. The oval c>'st with the worm coiled up inside is shown in figure 84. This type of cyst offers only a temporary lodgement for the cercaria, and it is evident that the worm must reach the definitive host soon if the infection is' to be successful. Cercaria micropJiarynx Faust 1917 Cercaria micropJiarynx is a minute larva of the xiphidiocercariae, oval in contour, with small clavate tail (Fig. 93). The body is covered with minute spines arranged in diamond pattern, progressively less prominent toward the caudal end. The spines are probably constant characters of the adult as weU as of the larva, since the entire trunk is well suppHed with these spines while the tail is naked. The body measures 0.18 mm. in length and 0.09 mm. in width. The tail is 0.14 mm. long and 0.03 mm. at the base. It is inserted into a caudal pocket provided with a group of spines on the lateral lappets ventral to the tail. The oral sucker is large for the bod}'- size, 35^1 in diameter, while the acetabulum is shghtly smaller, 30/i in diameter. Inserted in the hood of the oral sucker is the stylet organ (Figs. 91, 92), 34fi long and 5n to 6fi in breadth along the shaft. The organ is reinforced all around and has a velum stretched across the ventral surface of the quiU. The cercaria was secured from the infected Uver tissues of a large number of Lymnnea proxima, taken from Rattlesnake Creek, Missoula, in Novem- ber 1916 and in May 1917. The cercariae develop in oval irregular sporo- cysts, measuring 0.24 mm. along the long axis and 0.18 mm. along the short axis (Fig. 94). The body wall of the sporocyst consists of a single layer of epidermal cells, between which are found numerous excretory granules, lying in irregular grooved channels. There is no localization of the germinal epi- theUum, so that germ balls arise from aU portions of the body wall and, when mature, break out into the body lumen. Not only do the cercariae develop to maturity in the sporocyst, but in some cases they drop their tails and encyst in the sporocyst (Fig. 95). Thus the larval host, the snail, is the food of the intercalated or of the definitive host, since no free-living stage is com- monly found. In case the cercaria is pressed out of the sporocyst before encystment, it swims about for a very brief period, then drops the tail and enc>^sts. The excretory system consists of a subspherical vesicle and bellows-shaped comua, which open into the vesicle thru a common cylinder. The three usual tubes of the excretory system are present, the single posterior and the two anterior ones. The tail tube is single median, with a few inconspicuous lateral tributaries. The comua are filled with excretory fluids; they are Imed with cells (Fig. 98). The digestive system consists of the very minute pharynx in the mid- region of the esophagus, and two vesicular f urcae considerably anterior to the 75] LIFE HISTOR Y OF TREMA TODES—FA UST 75 acetabulum. No glands occur in the pharynx or cecal regions, but in the prepharynx region, just within the oral aperture, is a band of about fifty gob- let cells of a glandular nature. The salivary-mucin glands are found at the sides of the acetabulum. They consist of eight cells for each group. They are relatively large, vesicular, and have common ducts opening into the oral pocket. In addition to the usual transverse and longitudinal systems just within the integument (Fig. 97, 98), large muscle elements are scattered thruout the parenchyma. The genital organs (Fig. 96) consist of a prominent vagina, a well-defined Laurer's canal, and a group of massed organs in the vicinity of the ootype. In addition, there are the yolk follicles, distributed over a wide range of the dorsal side of the animal. The follicles are closely massed together. This species suggests a Plagiorchid genital system. Cercaria racemosa Faust 1917 Cercaria racemosa belongs to that group of stylet cercariae usually desig- nated as cercariae ornatae, by virtue of their possession of a fin-fold structure to the tail. While this separation may be concomitant with a deeper, more fundamental difference of type, it is well to bear in mind that fin-folds occur in other groups, such as in monostomes, Cercaria lophocerca (Fihppi, 1857:5; Fig. 3), echinostomes, Cercaria echinatoides Fil. (La Valette:1855,Taf. I, C), and among the furcocercous larvae, Cercaria cristata (La Valette, 1855,Taf. II, K). It may be looked on as a modification of the caudal organ for swim- ming. The body of Cercaria racemosa is elongate ovoid, measuring 0.29 mm. in length by 0.11 mm. in width (Fig. 100). It is characteristically broadest just ahead of the acetabulum. The tail consists of a central lanceolate region and a lateral ruffled fringe, which is most conspicuous at the distal end. The tail measures 0.22 mm. in length and 0.04 mm. in width at the base. It is inserted into the posterior extremity of the trunk, altho there are no lateral sinuses to be found in this caudal pocket. The acetabulum is sHghtly caudal to the middle of the body. It measures 26/i in diameter, while the larger oral sucker has a diameter of 36iu. The stylet organ (Figs. 101, 102) is delicately attenuate, with a reinforced tip. It is 27/i long and about 5^ wide at the base. The species was found in the liver of Lymnaea proxima in the chara sloughs of the Bitter Root River at Fort Missoula, Montana, in October 1916. It occurred as a minor infection along with C. dendritica and C. gracillima. The parthenita is an irregular polygonal sporocyst about 0.62 mm. long and 0.38 mm. thick (Figs. 104, 105). At one end is situated a pocket of glandular cells which attach the sporocyst to the host. This is done by the exudation of a mucus. It is doubtful if these cells are at all muscular. At the antipodal end is the germinal epithehum, from which germ balls arise. Only a few cercariae develop within the sporocyst at any one time. The bladder of the excretory system is truncate, with a common median vessel leading into it from the anterior end. Lining the vesicle at the anterior 76 ILLINOIS BIOLOGICAL MONOGRAPHS [76 end are six gland cells, paired right and left. They appear as small tubercules suspended from the anterior wall of the vesicle. Anterior to the median vessel are two cornua, elongate, yet swollen, reaching antero-laterad around the acetabulum. Near the acetabulum there are received the common posterior and the two anterior tubules. The pattern of the capillaries is racemose. The tail trunk system consists of a common median vessel with many lateral tubules. The entire system is filled with minute excretory granules. The digestive system consists of a very long esophagus, near the anterior end of which is the small sphincter, and from the posterior end of which the furcae arise. They extend partly around the acetabulum. The salivary-mucin glands consist of right and left paired groups of cells, eight to the group, with long ducts leading in a common bundle to the oral pocket. In the region of the cerebral ganglion a pair of oval bodies, the non-pig- mented eye-spots are located. They are degenerate, similar to those eyes described for Cercaria gracillima (p. 52). The genital cell masses are found in the region of the acetabulum (Figs. 104, 107). To the left is Laurer's canal, and running dextro-laterad is the closely coiled uterus. The genital pore is on the right of the mid-ventral line, anterior to the acetabulum. Running into the ootype from the postero- lateral angles are the vitelline ducts, connecting the vitellaria with the ootj'pe. The testes are not well defined. The relationship of the cercaria is not evi- dent from the genital cell masses. Cystogenous cell glands are present, altho not as conspicuous as in C. glandulosa or C. micro pharynx. Encystment takes place after a considerable period of free swimming life. Decaudation always precedes encystment. The cyst wall is thin ; the animal is easily viewed thru the cyst. Echinostome Cercariae Cercaria trisolenata Faust 1917 Cercaria trisolenata represents a unique type of echinostome larva (Fig. 109). It is more attenuate than the average species of this family, and has an unusually short tail. The body has an average length of 0.45 mm. and a width at the preacetabular region of 0 1 mm. The tail is about 0.2 mm. long, lanceolate, and measures 0.06 mm. at the base. An anterior region of the trunk, measuring 0.06 mm. along the median line, constitutes the head region, behind which is a neck-like constriction. There is a collar of 36 spines along the margin of the head, arranged in a single irregular series (Figs. 110, 111). These spines are bluntly rounded at the base and taper to a rounded point at the distal end. They are from 12/x to 14jLt in length. The body as a whole is usually covered with minute spines. The acetabulum is beset with an irregular arrangement of crooked spines (Fig. 112). The oral sucker is small but powerful, Z^ti in diameter. The acetabulum, situated behind the mid- plane of the body, measures 42)u. These cercariae, together with Cercaria gracillima, are the most cosmopoli- tan species of the Bitter Root River. They occur in Physa gyrina from the 77] LIFE HISTORY OF TREMATODES— FAUST 77 upper and lower reaches of the Valley, and in Planorbis trivolvis from the region of Buckhouse Bridge. The infection of the host is always heavy, both as relates to numbers of individuals infected and the number of parasites in the individual host. The per cent of infection ranges from 22 to 100. The parasite is located primarily in the interstices of the liver, but frequently invades the cecal walls and does great injury to the tissues. The cercaria develops in a redia of well-marked characters (Fig. 117). The redia measures about 1.0 mm. in length and has a mid-diameter of 0.22 mm. and a gross width of 0.35 mm. across the region of the locomotor feet. A small powerful pharynx at the anterior end opens into the rhabdocoel gut which fills the greater part of the body cavity, extending almost to the posterior extremity. The germinal epithehum is at the posterior end. From this layer the ova develop, which grow into cercariae. The first character of the germ ball to become diflferentiated superficially is the oral sucker (see series of stages in figure 114), Later the tail and the acetabulum become marked off, and finally the oral hood. At the posterior end a small, non-muscular, truncate bladder is situated. It opens anteriad into two simple unbranched tubes. These can be traced cephalad inside the intestinal ceca to the head of the worm. The cephalic end of the excretory system is unique. Lateral to the pharynx, a triangular channel-system is found. From the anterior angle a small capillary leads forward to a single flame cell. From each of the other two angles a small capillary leads back to a flame cell. This constitutes the trisolenate sys- tem at the anterior terminus of the excretory tract. The tail excretory tube is a single median structure and has no laterals or terminal outlet. This fact necessitates a revision of the scheme proposed by Cort (1915:37), in which this writer characterizes the excretory system of echinostome cercariae as "opening on each side of the anterior part of the tail. " It seems from the present investigation that the three flame cells in the anterior part of the trunk may be a more reasonable criterion for distinguishing the excretory system of this group. Further work on other forms must be done before this can be definitely proposed. Excretory granules fill the lateral excretory trunks from the pharynx region as far caudad as the acetabulum. The digestive system is simple. It consists of a long esophagus, with a very small pharynx sphincter about in its middle, and two very long furcae, extending to the sub-caudal region. The genital cell masses are yet very immature. There are four cell masses present, one on the upper right of the acetabulum (Fig. 130), the vagina; one^ behind the acetabulum (Fig. 131), the ovary, and two tandem masses in front of the bladder (Fig. 120), the testes. In the vicinity of the ovary are num- erous viteUine follicles, but they have not been found to follow any definite pattern. 78 ILLINOIS BIOLOGICAL MONOGRAPHS [78 The nervous system of this species has been made the basis of the dis- cussion on page 49, and needs no further consideration here. The musculature is ahnost all parietal, except for the walls of the intestinal tract. Parietal and splanchnic muscles are similar in structure. The former consist of external transverse and internal longitudinal bundles, while the latter consist of external longitudinal and internal transverse fibers (Figs. 118, 119). Each fiber can be traced to a myoblast, the central figure of which is the large oval nucleus, with karyosome and radiating processes, so that the whole figure appears stellate. There are several fibers originating from each myoblast; they always nm along a single axis. The longitudinal mus- cles of the tail are prominent (Fig. 133). The body is filled with a parenchyma complex, consisting of undifferen- tiated cells, connective tissue fibers, and cystogenous gland cells. In the tail of an immature cercaria (Fig. 133), there is a partition of parenchyma cells, separating the caudal excretory canals into right and left tubules. This condition disappears as the animal matures, altho vestiges of these cells may be found in the mature cercaria. The cystogenous cells are differentiated parenchyma cells, filled with a mucoid in the form of oval granules. In the ordinary cystogenous cell (Fig. 113), the granules are about l/i by 0.6/i in section. There is a central nucleus to each of these cells, with poorly defined membrane separating it from the cytoplasm. It is conspicuous because of its large number of chromatic gran- ules, composed of elongate flecks. These flecks are also present in considerable numbers thruout the cytoplasm; they are especially massed against the cell walls. The glands are best developed in the middle of the body (Fig, 109, sections hb and dd). Since the cystogenous glands are well developed, the cyst wall is heavy (Fig. 115, A-C). In crawling over the surface of any object the mature cercaria squeezes off the tail by a constriction of the posterior transverse muscles. A final jerk of the tail frees it from the body. Immedi- ately the cystogenous glands pour out a mucus aroimd the contracting worm, so that at first an oval cyst is formed. Later, as it hardens, it assumes a more spherical outline (Fig. 116). Thru this cyst membrane the excretory and digestive systems of the body and the collar spines are readily distinguished. The cysts are so well walled and so numerous that they suggest a considerable period of wintering over. Cercaria biflexa Faust 1917 Cercaria biflexa belongs to a type of echinostome cercariae distinguished by a smooth body outline, a long powerful taU, blunt oral hood spines and a reflexed excretory tube. The excretory system worked out by Looss (1894: Fig. 191c) for Distomum echinatum approaches the system in this species to some extent, but differs from it in many details. The body of Cercaria biflexa is elongate ovoid, with a slight constriction just behind the oral hood (Figs. 134, 135). Both the body and the tail are extraordinarily muscular. The body measures 0.45 mm. to 0.5 mm. in length 79] UFE HISTORY OF T REM ATODES— FAUST 79 and 0.13 mm. to 0.15 mm. in width. The tail is at least as long as the body or slightly longer. Its width is about 0.05 mm. at the base. The oral sucker has a diameter of 55At and the ventral sucker, situated at the beginning of the posterior third of the body, measures 65/* in diameter. Around the oral hood is a circlet of collar spines, 42 in number, ovoid elongate, bluntly rounded at both ends, with a length of 10/t to 15/1 and a thickness of 3/i. The worm was found in Physa gyrina in November 1916, and in Planorhis trivolvis in May 1917, in the neighborhood of Buckhouse Bridge, near Fort Missoula, Montana. The parthenita is a redia with a length measurement of 0.4 mm. and a thickness of 0.088 mm. (Fig. 137). The locomotor feet are short, blunt pro- cesses in the posterior third of the body, and have a gross span of 0.1 mm. In contrast to the large gut-pouch of Cercaria trisolenata parthenitae, the rediae of this species have short inconspicuous rhabdocoel guts, only 0.1 mm. in length. One-third of this is occupied by the pharynx. The body wall is covered with a thick integument, within which is a heavy muscular layer. At the posterior end are a number of small spinous projections (Fig. 141). The germinal epithelium also is at the posterior end. A noticeable feature of the cleaving ova is their flattened condition (Fig. 141). Stages in matura- tion and cleavage are seen in this figure and may be compared with similar stages of maturation and development in C. trisolenata (Fig. 140.) The cer- cariae, when mature, escape thru the birth-pore situated ventrolaterad. A prominent excretory system is foimd in this cercaria (Fig. 135). The vesicle is a cylindrical organ inflated posteriorly. It is not muscular to any marked degree. Tubular cornua empty into the anterior end of the bladder. As these cornua are traced forward lateral tributaries are found to empty into them at regular intervals. In the region of the pharynx the tubes become attenuated and bend twice upon themselves (Fig. 138) . The detailed descrip- tion of this anterior end of the system of Cercaria biflexa is found in the section on morphology (p. 40). It may be noted here that there are three flame cells along the course of the ultimate tubule of the system, and that these seem comparable to the three flame cells found in C. trisolenata. The excretory tube in the tail is a single median tube for about two-fifths of the way distad, at which point it forks and continues double the remainder of the way distad, with numerous cross-anastomoses. It does not open to the outside either on the sides or end. The digestive system consists of an extremely long esophagus, extending all the way to the acetabulum; furcae which end at the caudal end of the animal; and salivary-mucin glands, developed to a very high degree. These latter consist of an inner and an outer series of right and left groups (Fig. 134). There are from fifty to sixty cells in each group, in oblong clusters, with a common duct anterior to each series leading cephalad. The two ducts of each side fuse to form a single lateral duct which leads into the oral pocket. These glands are different from the majority of mucin glands in being differentiated 80 ILUNOIS BIOLOGICAL MONOGRAPHS ^ into inner and outer series. The condition is similar in part to that in Cer- carta crenaia (Fig. 55), in which species there is also a double series of glands on each side of the esophagus. But in this case the glands of the inner and outer series are not different in structure and function as in C. crenata. Here, too, the ducts are not composed of a bundle of separate ducts, as is found in C. marcianae (La Rue, 1917:5), but consist of a single common duct for the entire group of gland cells. The genital system is much further developed in this species than in C. trisolenata (Fig. 139). Behind the acetabulum is the ovary, from which a uterus leads around the acetabulum, ending in a swollen vagina in the pre- acetabular region. Only the transverse ducts of the vitelline system are differentiated. Behind these are the two testes, unequal in size, one above the other. The encystment of Cercaria biflexa is similar to that of C. trisolenata in that it depends on the secretion of mucoids from a large number of cystogenous glands in the parenchyma. It differs, however, in the two species both as to time and place of encystment. Cercaria trisolenata encysts only after it has escaped from the liver tissues of the host. C. biflexa encysts within the host, immedi- ately upon breaking thru the birth-pore of the redia. Thus a section of Planorbis trivolvis liver tissue shows the interstices of the Hver ceca filled with encysted cercariae, which continue to grow and differentiate within the pri- mary host (Fig. 159). Furcocercariae Cercaria graciUima Faust 1917 Cercaria graciUima is a furcocercous cercaria more slender than those previously described. This species, together with C. tuberistoma (p. 82), constitute the second instance of furcocercous cercariae to be described for North America, the first being C. douthiUi Cort (1915:50-52; Figs. 55-64). In addition to the forked-tail character of these three species, they lack a pharynx, and have paired salivary-mucin glands leading into the oral pocket, composed of four or more cells to each group. The "eyelet" excretor>' ana- stomosis, connecting the excretory system of the body and the tail is also a common character. Cercaria graciUima has an oblong cylindrical body (Fig. 142). The branched portion of the tail is elongate lanceolate. The body length varies from 0.13 mm. to 0.16 mm. and the diameter of the worm varies from 0.02 mm. to 0.03 mm. The unbranched portion of the tail is about 0.16 mm. long and the caudal rami are of equal length. The former is 0.02 mm. to 0.03 mm. in diameter and the ramus has a width of 0.01 mm. The trunk is characterized further by the absence of a true oral disc, while in its place there is an invertible sucker. A ventral sucker, 12fi in diameter, varies in location, according to the movements of the animal, from the middle of the ventral side to a position considerably farther forward. The cephalic region is ovately rounded when the sucker is fully distended and is crowned by a cap of small spines. A 81] LIFE HISTORY OF TREMATODES— FAUST 81 feature of this cercaria, in common with that of C. douthitti, is the possession of eye-spots (Figs. 144, 150). But the eye-spots of C. gracillima are the more vestigial, for they have no pigment. This species was found in the livers of Fhysa gyrina Say, collected from the lower reaches of the Bitter Root River near Maclay Bridge, Buckhouse Bridge, and the sloughs at the Roadhouse, near Fort Missoula, in the fall of 1916. In addition it was found in the livers of Lymnaea proxima Lea from Rattlesnake Creek, Missoula. The infection in most cases was not exceed- ingly heavy, except in the collection from the sloughs at the Roadhouse, where thirty-three out of seventy-one individuals were infected, or 46.5 per cent. The cercariae develop in long cylindrical sporocysts, varying in length from 0.25 mm. to 0.1 mm., but most frequently averaging about 0.5 mm. (Figs. 146, 147). In diameter the sporocysts vary from 0.2 mm. to 0.4 mm. The parthenita is a simple structure, non-muscular, depending on the daughter cercariae for its movement. At one end (Fig. 147) is a non-muscular attach- ment area; at the other end, merely a rounded non-differentiated cap. The germinal epithehum is localized at the attachment end. From this mass the daughter worms develop. Internal pressure from the developing larvae increases the length and diameter of the parthenita. In development (Fig, 148), the ovoid germ ball first differentiates a tail portion; later the rami appear. It is not until considerably later that the acetabulum is found. The oral spines appear only when the larva is mature. The movement of the cercaria is characteristic for furcocercariae. The main movement consists in a very strenuous beating and lashing of the rami, so that the head is pushed into the object with which it comes in contact. In case the head is not forced into the object, the worm is set free by a back- ward movement of the tail and the entire worm squirms around until it comes in contact with another object, when the same boring movement is again attempted. The oral end of the cercaria is much better adapted to this type of invasion of the tissues to be infected than if it possessed an oral disc. The excretory system of C. gracillima is embryologically a single paired system for both body and tail. As development and differentiation of parts progress the tubes in the posterior extremity of the trunk and the anterior region of the tail fuse, to form a median bladder and the common tube of the proximal region of the tail. There remains the bifurcated portion in the laterals of the trunk and the rami of the tail, and in addition, the "eyelet anastomosis." This eyelet structure has been observed by Looss (1896:172- 174; PL 15), m Cercaria vivax Sons, and by Cort (1915, Fig. 57) in C. douthitti. The excretory system in the body consists of two lateral tubes that diverge from the bladder and can be traced forward, together with dendritic tubules and capillaries, the internal ones of which frequently form chiasmic anasto- moses across the median plane of the body. Slightly posterior to the middle of the body the lateral tube expands and opens into a pocket provided with 82 ILLINOIS BIOLOGICAL MONOGRAPHS [82 dlia (Fig. 145). These cilia come from a flame cell bordering on the lumen of the lateral tube. A second pocket somewhat anterior is an atrium into which many of the capillaries empty; it is filled with small excretory granules, in this way acting as a secondary reservoir. The digestive system of C. gracillima consists of an unbranched esophagus without a pharynx sphincter, a pair of short degenerate furcae extending posteriad beyond the acetabulum, and a ring of gland cells in the region of the esophagus where the pharynx might be expected. Opening into the oral atrium thru common bundles of ducts are the salivary-mucin glands (Fig. 144). These glands are very large with vesicular nuclei. They are situated in the posterior third of the body. In cross section the ducts are similar to those described by Cort (1915, Figs. 59-62) for C. douthUti. The nervous system has been discussed on page 54. The genital cell masses in the cercaria are hermaphroditic (Fig. 149). Anterior to the acetabulum are the vagina and the cirrus pouch buds, and lateral, extending both anteriad and posteriad, are the viteUine foUicles. In the posterior extremity is a conical germinal mass, from which are proliferated anteriad a number of small testicular folMcles. The general features of this fluke make it possible to refer it to the Schis- tosomatidae. Cercaria tuberistoma Faust 1917 This species of cercaria is shorter and much more muscular than C. gracil- lima. The body is elongate ovoid, with the anterior end slightly constricted and crowned with a pair of tuberosities (Fig. 155). The body length is about 0.2 mm. and the width 0.05 mm. to 0.06 mm. The tail measures about 0.32 mm. as a whole, equally divided into common portion and rami. There is no oral suctorial disc, but instead the oral invertible proboscis. The acetabulum measures 0.03 mm. in diameter. The cercaria was secured from a single Ught infection of Physa gyrina collected in the Bitter Root River at Corvallis, Montana, in October 1916. Out of nineteen snails examined only one was infected. Only a few cercariae were secured, and these were studied as Hve mounts. From this study the excretory, digestive and general body features were worked out. The cercaria develops in an elongate, dumb-bell-shaped sporocyst, spread- ing out at one end to form an attachment disc (Figs. 157, 158). At the end opposite the attachment organ the cercariae develop from the maturation of the germinal epithehum. They escape thru a rent in the wall of the sporo- cyst. Stages in development (Fig. 158, A-E) are similar to those described for C. gracillima (Fig. 143). On the whole the embryos of this species are stouter than those of C. gracillima. The excretory system has the features common to all furcocercariae. The bladder and the eyelet are muscular (Fig. 155). The lateral tubes are of small diameter, with anterior and posterior tubules. No anastomoses take 83] UFE HISTORY OF TREMA TODES—FA UST 83 place in the cercariae of this species. The median tail tube receives six lateral tributaries, the anteriormost of which is reflexed. The rami have each an unbranched tubule. The cephalic region is marked by a large invertible sucker, extending thru the anterior third of the body. No intestinal ceca whatever have been observed in this species. No glands surround the esophagus as a distinct ring, altho the entire esophageal tube lining is glandular in nature. Four small salivary-mucin glands are situated in the posterior third of the body (Fig. 155). Their thick ducts empty into the oral cavity as heavy bundles. The cells of this system are filled with closely aggregated, deeply staining granules. The nucleus of the salivary-mucin gland cell is extremely small. This species possesses neither pigment eye nor eye-spot without pigment. Encystment has not been observed in this species. Cercaria tuberistoma is probably a schistosomatid larva. 84 ILLINOIS BIOLOGICAL MONOGRAPHS [84 PATHOLOGY The infection in any case of internal parasitism suggests an inquiry as to the effects of the parasite on the host. The injury on the human sub- ject produced by trematode infections has been the subject of numerous observations and records. Notable among these are the contributions of Looss (1913) on Schistosoma haematobium, Katsurada (1914) on Schistosoma japonicum, and Ward (1909) on Fasciolopsis spp. Again, the effect of tre- matodes on their host has been the subject of considerable study in fish infec- tion, on account of the economic importance of the problem. But -where the special incentives to the problem have been lacking, very little study has been made on the pathological significance of trematode infection. The helminth parasite causes a two-fold injury to the host, mechanical and chemical. The inclusion of parasites within the organs of the host is the occasion for distension of the organs and consequent irritation; the piercing of organs of the host by the armature of the worm, an actual mechanical, injury. These injuries are accompanied by the formation of fibromata within the organs and, usually, attempts to isolate the parasite by the secretion of a cyst around it, as in schistosomiasis (Bovaird and Cecil, 1914:191). In the ordinary infection a toxin is secreted by the parasite, and frequently an anti- thrombin and a hemolysin are produced. Such injuries as these in higher animals are diagnosed by the blood-picture, where excessive hemocytolysis and eosinophilia are found. The infected organs of the molluscan hosts of the Bitter Root Valley are the liver ceca. Altho these Ue next to the testes, the worms have never been found to invade these organs. Thomas (1883:114) found that the cercariae of Fasciola hepatica live normally in the pulmonary chamber of the snail Lymnaea trunculata. Cort (1915) found the infected organs of the Campelomas were the gills, but in other species, the Hver tissues were the seat of the infec- tion. The infected tissue of the Venezuelan snail, Planorhis guadelupensis, is the testicle according to observations made by the writer. The liver ceca consist of polygonal lymphocytoidal cells grouped around the liunina of the ceca, with an epithelial Uning surrounding the ceca. Among the ceca are large interstices filled with lymph. These intercecal spaces are the places where the worms are first found, suggesting invasion thru the blood stream. In light infections, the parthenitae lie here, absorbing the nourish- ment from the surrounding liquid in which the worm is bathed. Ths only mechanical injury up to the time of the activity of the cercariae is caused by the agitation of the developing larvae encysted within the host. But in the case of heavy infection, especially where the larva does not encyst within the host, where it works its way out into the water, even a few worms may cause considerable mechanical harm to the host. In an examination of living material and sections of infected moUusk Uver tissue, no infection was found to be so light that the host was unharmed. In 85] LIFE HISTORY OF TREMA TODES—FA UST 85 the Cercaria hiflexa infection of Physa gyrina (Fig. 159), where the cyst mem- brane is moderately heavy, many ceca are uninjured, yet some betray the marks of injury. One such injury is shown in the figure. In this case the cells of the ceca have undergone only a little change. A comparison of this condition with that of C. micropharynx infection in Lymnaea proxima (Fig. 160) and C. gracillima infection in Physa gyrina (Fig. 161), shows a compara- tively small injury in the former tissue and a severe injury in the latter tis- sues. Both the latter cases show tissue degeneration. The chemical change in Lymnaea proxima is evinced by 1) fatty bodies that have accumulated in some of the cells (a), showing as highly refractive inter-cellular inclusions; 2) large vacuoles in the cells (6), especially around the nuclei; 3) cytolysis and karyolysis (c, d), including a sloughing of the tissues in the region of the lumina of the ceca. The condition of C. gracillima infection in Physa gyrina (Fig. 161) pictures a further degeneration of the tissues. Fatty globules {b), are common, usually accumulated as spherules within the wall. Vacuolization {d) has progressed to an advanced stage. Cytolysis and karyolysis (a, c) have gone so far that the outlines of the majority of the cells are indistinct and no difference exists longer between the epitheUal and the lymphocytoidal cells. An indefinite, irregular margin marks off the ceca from the interstices in which the cercariae lie. A further change consists in the formation of fibromata {e) and granulomata within the degenerating ceca. Finally the epithehum surrounding the entire liver mass has been penetrated by sand granules (/), and other foreign bodies have had access to the tissues. In the infection of Planorbis irivolvis with C. trisolenata the mass of the worms was about twice that of the Uver tissue infected. The tissue was so distended with the parasites that a prick of the needle was sufficient to cause the liver membrane to burst, upon which the rediae and cercariae fairly poured out of the tissue. The data on the effect of the trematode infection on the molluscan host are significant. No infection is so light that mechanical and chemical injuries are not inflicted. In the heavy infections such as are conmion to the moUusks of the Bitter Root Valley, the injury is so heavy that it must alter appreciably the Hfe of the host. The mechanical pressure tends to inhibit or increase the functioning of the glandular organs and cramps the tissues within unusual confines. The presence of foreign proteins in close association with the lymph sinuses is sufficient to alter the vital economy of the host. The boring of the worm destroys the tissues locally and in general irritates the mechanism, exposing it to bacterial infection. The secretion of digestive juices by the parasite, and of anti-thrombins and possibly specific poisons, upsets the entire physiological equilibrium of the organism. 86 ILUNOIS BIOLOGICAL MONOGRAPHS [86 PROBLEMS PRESENTED INTERRELATION OF TREMATODES In working out new species of organisms, especially from new geographi- cal areas, there are often physiological and morphological facts that are of general significance in the light of previous studies. Relationship is the ultimate problem for all workers in morphology. While light is shed on phylogeny by the discovery of new species, it is futile to expect to found a system of phylogeny on a single species. With these limitations in mind the writer presents some of the more important questions that arise from the study of the trematodes of the mollusks of the Bitter Root Valley. In the early days cercariae and rediae were considered as different groups of the animal kingdom, and it was not until the life-history studies of Leuckart, La Valette (1855), and Ercolani (1881, 1882) had been pubUshed that the genetic relationships of cercariae and parthenitae were established. The germ layers of all generations of trematodes have a similar origin, and impor- tant structures of the group present the same problem. Certain investigators of recent time have come to regard the trematodes as a polyphyletic group. Their conclusion has resulted, perhaps, from their lack of study and consequent inability to recognize the fimdamental resem- blance of the genital, excretory and nervous systems of the various sub-divi- sions of the group, especially dming the developmental stages. From more convincing observations Odhner (1907) has concluded that the Monostomata are poU'phyletic. He has noted among certain monostomes a structure comparable to the pharyngeal pockets of amphistomes, and among others a primitive acetabulum (1911). In a study of monostome cercariae from the Bitter Root Valley, the similarity of the nervous system and genital cell masses of Cercaria peUucida and of those systems in Gastrothylax gre- garius Looss has been investigated. Both Cercaria peUucida and Gastrothylax gregarius show paired brain ganglia closely set together with only slight constriction of the dorsal com- missure. In both species the nerve cells lie superficially upon the central nerve gangUon masses. IVIoreover, relatively large posterior ventral and smaller lateral and dorsal tnmks, together with their respective positions, constitute a series of similarities not to be overlooked. The lack of pharyn- gealis, palatinus, and dorsolateral commissure (Figs. 123, 124) serves to show that the nerve complex of the monostome larva Cercaria pdlucida is not t>'pically distomate. Its nerve structures are much more readily referred to the Gastrothylax type. In the second place certain features of the genitalia of Cercaria peUucida and Gastrothylax suggest a common ancestry. The median ovar>' in the subcaudal region; the paired testes lateral to the ovary; the dendritic vitel- laria, located in two series, and, finally, the parallel course of the uterus and 87] LIFE HISTOR Y OF TREMA TODES—FA UST 87 the vas efferens to the genital pore far cephalad — ^all of these show in common a genital system quite distinct from the usual distome types. The similarity of the nervous and genital complexes of larval monostomes, such as Cercaria pellucida and C. konadensis, and the amphistome, Gastro- thylax gregarius, suggest a common origin of certain monostomes and amphi- stomes. Among adult distomes there is great variety of structure, yet only in one family, the Schistosomatidae, has the nervous system been fundamentally altered. The structures of the two furcocercous larvae, Cercaria gracilUma and C. tuberistoma, demonstrate their relationship to the Schistosomatidae. The reasons for this beUef are these: The characters which distinguish the apharyngeal furcocercous cercariae are as follows: 1) a forked tail (larval character only); 2) paired groups of salivary-mucin glands (larval); 3) absence of an oral suctorial disc, and in its place 4) an invertible suctorial proboscis; 5) an apharyngeal esophagus, pro- vided with glands in the region usually occupied by a pharynx. The nervous system, more deeply seated, is modified by the degeneration of the posterior laterales during early embryonic development, and the fusion of the posterior dorsales with the posterior ventrales about one-third the body length back from !the anterior end (Fig. 150). All of these, except the forked tail and the saUvary-mucin glands, are both larval and adult characters. In addi- tion, the larva of Cercaria gracilUma has several testicular follicles proliferated from the testes-mass at the posterior end of the body. Certain of the structures of this group also characterize the larvae of other groups of trematodes. For example, Cercaria cristata La Val. (1855:23; Taf. II, Fig. K), has a bifid tail and apparently lacks a pharynx, but the fact that it lacks an acetabulum probably separates it from the distome f urcocercariae. Among the Gorgorderinae there are apharyngeal cercariae with several testes. However, Ssinitzin (1905:46-51; Taf. I, II) has shown for four Gorgordera species, that the cercariae are characterized in common by 1) a stylet, 2) salivary glands only in the cephalic region of the body, 3) a large glandular excretory vesicle, almost filling the posterior third of the body, and 4) a dis- proportionately large tail, showing the cystocercous relation of the larvae of the group. Moreover, the nervous system of the Gorgorderinae is typically distomate (Zailer 1914:386). It may be stated with considerable probabihty that all of the fundamental organs of the f urcocercariae, namely, the apharyngeal esophagus, the multiple testes, and the uniquely modified nervous system, are found in only one family, the Schistosomatidae. All described Schistosomatidae are charac- terized by the absence of a true oral suctorial disc and by the presence of an invertible oral suctorial pouch. They have no pharynx, but in its stead glands that line the wall of the esophagus. Looss has described the modified nervous system of the family in his study of Schistosoma haematobium (1895: 88 ILLINOIS BIOLOGICAL MONOGRAPHS [88 60-68; Taf. II, Fig. 18). It corresponds in detail to the system in Cercaria gracilUma previously described. Coupled with these morphological likenesses are the experimental data of Leiper (1915, 1916), Miyuri and Suzuki (1914), and Iturbe and Gonzalez (1917) on Schistosoma life-histories. Leiper has found that the three schistosome species known to infect man, Schistosoma haematobium, S. man- soni, and S. japonicum, give rise to miracidia which have a certain attraction for certain snails in the districts infected. Within the tissues of these snails the miracidia metamorphose into sporocysts, and the second generation sporo- cysts give rise internally to bifid cercariae with a ventral sucker but without a true pharynx. Furthermore, these cercariae introduced thru the skin of experimental animals, mice and monkeys, give rise to typical unisexual adult schistosomes. This two-fold evidence favors the view that the furcocercous apharyngeal distome cercariae, including Cercaria gracillima and C. tuberistoma of the Bitter Root fauna, develop, under proper conditions, into adult schistosomes. One character figured by Leiper for all of his apharyngeal bifid cercariae, yet not used by him as a diagnostic character, is the presence of saUvary-mucin glands. On the other hand, one character used by Leiper for cercariae of the group, namely, the absence of a pigment eye, holds for his three species of schistosome larvae, but does not hold for Cercaria ocellata La Val., C. douthitti Cort, or C. gracillima. It has been shown that the eye-spot may be present without pigment (C gracillima). Likewise the failure of Looss to mention an eye- spot for C. vivax Sons. (1896:216-223; Figs. 172-174) does not necessarily imply the absence of pigmentless eye-spots in that species. The relationship of the forked tail apharyngeal distome cercariae will be made much clearer by a consideration of the genital organs. The adult Schis- tosomas into which the larvae of Leiper develop are characterized by a relatively small number of testicular folUcles, 4 to 5 for S. haematobium, 6 to 8 for .5. japonicum, and 8 for S. mansoni. On the other hand, the testicle prolifera- tion in Cercaria gracillima (Fig. 149) shows twenty-four or twenty-five fol- licles already differentiated from a posterior germ mass. The large number of testicular follicles has been found to be characteristic of the adult Schisto- somatidae of the genera Bilharziella (Kowalewski,1895; 1896), Gigantobil- harzia (Odhner, 1912), and Ornithobilharzia (Odhner, 1912). None of these genera and in fact no Schistosomatidae have been reported from North America. From these considerations it seems probable that Cercaria gracillima is the larva of a schistosome genus, such as Bilharziella, Ornithobilharzia or Gigantobilharzia, all of which are bird parasites. Since the germinal masses of Cercaria gracillima are hermaphroditic, and any marked differentiation of the organs does not take place while the larva is outside the definitive host, differentiation of sex in Schistosomatidae takes place in these species comparatively late in their metamorphosis. This view 89] LIFE HISTORY OF TREMA TODES—FA UST 89 is in keeping with the studies of Odhner (1912), who points out the fundamen- tal morphological relationship of the hermaphroditic species Liolope and Haplometra to the unisexual BUharziella, Gigantobilharzia, Omithobilharzia, and Schistosoma. The discussion leads to the conclusion that the furcocercous larvae possess in common 1) a bifid tail, 2) a ventral sucker, 3) an oral suctorial pouch which can be inverted, 4) a glandular esophagus without sphincter muscles, 5) paired groups of salivary-mucin glands, four or more to the group, 6) multiple testes, and 7) a specifically modified nervous system. In the light of present knowledge all of these species fall within the limits of the family Schistoso- matidae. Of all the known groups of trematodes the Holostomata have been the group of least genetic study and most erroneous interpretation. On account of their large size the adult holostomes have been known for many years and dozens of species have been described. Nothing, however, has been known of the parthenitae and their development. Without sufficient evidence Brandes (1891:573) has interpreted the sketch of a miracidium of Strigea (Holostomum) cornucopiae Molin (von Linstow,1877, Fig.30) as a metamorphos- ing tetracotyle. In other words, Brandes concludes that the holostome has a direct development without the intercalation of a parthenogenetic cycle. Ercolani (1881:284-290; Tav. II, Figs. 16-22) has worked out the life-history of Strigea erratica (Duj.) from the tetracotyle to the adult form, by infecting Anas sp. with Tetracotyle typica cysts from the mollusk Planorhis corneus. Altho Ercolani found a tetracotyle in a sporocyst (Tav. II, Fig. 18), he inter- preted it as the invasion of the tetracotyle into the sporocyst of Cercaria ocellata La. Ya\. Ssinitzin (1910:22, 23) has justly criticized Brandes' con- clusion of the monogenetic development of holostomes, but in lieu of true holostome evidence in support of the digenetic view he has substituted evidence from Cercaria plicata, a peculiar distome larva which he has found to bear certain relationships to the holostomes. It has been shown in this paper (p. 16) that there are parthenogenetic cycles in Cercaria flabelliformis, a typical holostome, and that several genera- tions of rediae are intercalated between the miracidium and the tetracotyle. Thus, there is conclusive proof that the holostome has an alternation of genera- tions, hermaphroditic and parthenogenetic, similar in kind to such alternation in other Digenea. In spite of the strangely modified suctorial apparatus and posterior genital organs of the holostomes, there seem to be good grounds for beUeving that they originated from the distomes. They have an acetabulum, and frequently the muscular rudiment of a genital pore just in front of the acetabulum (Fig. 52). On the other hand it is very doubtful if the lappets (Zapfenlappen of Brandes 1892, Taf. 41, Figs. 5-15) bear any homology to the genital pore rudiment. It has been shown, in fact, that the lateral lappets in Cercaria flabelliformis arise from a pair of oval suctorial grooves (Fig. 41), and that in 90 ILLINOIS BIOLOGICAL MONOGRAPHS pO Tetracotyle pipientis (Fig. 47), where these grooves remain rudimentary, no I ateral lappets develop. As von Linstow (1877:189) pointed out, species characters in Strigea (Holostomum) have been treated very superficially, since the group members are not readily distinguished by external markings and the internal anatomy is difficult to interpret. Yet the writer has found that even in the early larva the points of differentiation are well marked. The parthenogenetic egg of the holostome developing into the cercaria is at the time of matura- tion structurally different from the ova developing into a redia. Thus the actual phylogenetic history of the group is hidden by its precocity and the developmental stages of the holostome show only in telescopic fashion the actual ancestral history. Extraordinary nerve modification in the holostomes (Fig. 53) is related directly to the modification of the muscle complex. This modification con- sists usually in the degeneration of the posterior dorsales and laterales, and a relative increase in size and importance of the posterior ventrales. The other systems of the holostomes, especially the genital and excretory organs, are equally highly modified and equally well formed in the larva. Ssinitzin (1910, 1911) has suggested that the change in the genital pore from the pre- acetabular position to the posterior ventral extremity has come about thru the formation of a new opening rather than thru a shifting of the old pre- acetabular pore. The original pore is still present in the larvae, altho in most cases there is no clue to its former connection or function. The extent of these changes indicates a long period of gradual adjustment to a modifying environment. The study of the cercariae of the various groups of the Digenea not only serves to supplement relationship studies in adult hermaphroditic generations of trematodes, but also brings out structural relationships very considerably if not entirely hidden in the adult. The most constant of all the systems in the group Digenea is the nervous system. Any marked modification from the characteristic distomate type is indicative of a considerable period of divergent growth. The fundamental systems of the hermaphroditic generation of the tre- matode are deep seated; they are well formed in the cercaria, and little signi- ficant differentiation takes place during metamorphosis. RELATION OF TREMATODES TO OTHER GROUPS Among the early systematists Trematoda were classified with the Hiru- dinea because of the common superficial resemblance of the two groups. Even as late as 1871 Schmarda separated the Trematoda from the Turbellaria and Cestoda, and placed them with the Hirudinea in the Cotylidea. Balfour (1881:316, 317) considered a direct relationship of all Metazoa above Coel- enterata entirely unsatisfactory and conceived the idea of referring them all back to the trochophore larva which possessed radial symmetry. In his 91] LIFE HISTOR Y OF TREMA TODES—FA UST 91 monograph on Amphistomum subclavatum, Looss (1892:156, 157) com- pared the proHferation of the germ-balls from the body wall of the parthenita to the production of eggs and spermatozoa in the marine polychaetes, and suggested that other embryonic structures of the trematode were comparable to annelid structures, so that they might be considered of phylogenetic value. Recently Ssinitzin (1911:86) has spoken of the resemblance of the Trematoda to Arthropoda and Trochelminthes, in view of the absence of any ciliary integ- ument, in place of which, he says, the cuticula and the external skeleton develop. During this time the theory of the common descent of the Trematoda, Cestoda and Turbellaria has been gaining ground, not because they are all "flatworms, " as Ssinitzin insists, but on the homologies of the genital, excretory and nervous systems. The observations of Leuckart (1886:140), Schulze (1853:178-195), and Schneider (1864:590-597) all support this view, while Leuckart even saw the analogy between the gutless sporocyst and the Acoela. Lang (1884:669) showed that the nervous system of the Trematoda and Turbellaria was homologous. With the work of Haswell on Temnocephala (1888) the close affinities of the Trematoda and the Turbellaria became evident. In this group the excretory system, the three anterior and posterior nerve trunks, the anterior mouth, and the dorsal pigment eyes — all these bridged the way for the ac- ceptance of the thesis that the Trematoda and the Turbellaria have a common ancestry. The study of the parthenogenetic generations of the Digenea, to which this paper is devoted, stands in support of this thesis and contributes the following facts towards its further acceptance. 1. The body cavity of the hermaphroditic generations of trematodes and of Turbellaria is filled with differentiated mesenchyme and connective tissue. In the parthenitae the parenchyma is confined to the body wall because it is less diJGferentiated. 2. Both Trematoda and Turbellaria are typically flat, with a pronounced bilateral symmetry. The cylindrical appearance of the parthenitae is a secondary modification due to parasitism. 3. The epidermis of Trematoda and Turbellaria consists of a single layer of cells. In the sporocyst larva, the miracidium, and in the Turbellaria, the epithelial layer is ciliated. In the rediae and in the cercariae the layer is usually sloughed off before maturity and in its place the basement membrane of mesodermal origin, serves as the integument. 4. The nervous system of the Monogenea, the Digenea, and the Turbellaria is reducible to a common type. Two brain gangha with a transverse commis- sure, three anterior pairs of nerve trunks, and three anterior pairs of nerve trunks — these are common to all three groups. Moreover, the pigment eye- spots of the Turbellaria, Monogenea, and Digenea are not only homologous, but practically identical in detail (Hesse 1897; and page 52 this paper). In 92 ILLINOIS BIOLOGICAL MONOGRAPHS [92 each case one or more ganglion cells fill the optic cup. In each it can be traced to the brain center. Parasitism has caused the pigment eye to degen- erate in most adult Digenea. Even in the cercariae it is pigmented only in certain species; other species have lost all traces of pigment, but the optic nerve is still present and can be traced to the brain center. In many cases it has been lost, even in the cercariae. Eye-spots are common in miracidia, but are lost on metamorphosis into the sporocyst. There are no records of eyes in rediae. 5. The digestive tract of the cercariae and the adult hermaphroditic genera- tions of trematodes is usually triclad. In the redia the gut is rhabdocoel; there is a pharynx and saUvary glands have been described (Ssinitzin, 1911, and pp. 63, this paper). In the miracidium, there is an indication of a rhabdocoel gut and salivary glands (Looss, 1892; Miyuri and Suzuki, 1914), altho these are usually lost in the adult. In the Turbellaria the gut is triclad, polyclad, rhabdocoel or acoel. The pharynx is ordinarily present and salivary glands are common. 6. The excretory system in the two groups is at first a single pair of pro- tonephridia. This condition is found in miracidia, rediae, cercariae and Tur- bellaria alike. The capillaries, whether in the larva or adult, end in flame cells. 7. The genital system was one of the first in which investigators recog- nized the relationship between the Trematoda and the Turbellaria. The hermaphroditic condition in the hermaphroditic generation of the Trematoda is strikingly similar to that of the Turbellaria, with the common genital atrium in all groups except Acoela. Parthenogenesis in parthenitae is the result of the great change in environment of these cycles. Thus the main trend of investigation has come to support the common origin of the Trematoda and the Turbellaria. LIFE CYCLE OF THE DIGENETIC TREMATODES The life-history of the trematode of the order Digenea consists not in an alternation of sexual and asexual generations, but rather of successive sexual generations which are parthenogenetic and hermaphroditic. A problem which has arisen in connection with the genitaUa of the Digenea is the significance of Laurer's canal. Looss (1893a) considers it homologous to the uterus of Cestoda, while Goto (1893) beHeves it to be the homolog of the blind vagina of AmphiUna and the genito-intestinal canal of Monogenea. According to Liihe (1909) a Laurer's canal is present in Monostomes, and in some groups of the distomes, including Plagiorchiidae and Echinostomidae. It has not been recorded for holostomes or Schistosomatidae. Except for the Echinostomid cercariae, a Laurer's canal has been found in all cercariae of the groups studied by the writer, where the adult trematode has the canal. Absence of the canal in Echinostomid cercariae can be explained on the basis of late development of the genital organs in this family. On the other 93 J LIFE HISTOR Y OF TREMA TODES—FA UST 93 hand, no Laurer's canal has been found in the groups where no canal is present in the adult. Students of cercariae have not as a rule recorded the canal in trematode larvae. Ssinitzin (1905, Figs. 62, 67, 74) has found it in the three xiphidiocercariae, Cercaria gibba de Fil., C. prima, and C. secunda. The constant development of this organ in the several groups described in this paper shows that the canal originally had an important place in the genital processes of the Digenea. The pronounced difference in structure between parthenogenetic ova which develop into rediae and those which develop into cercariae has been discussed (p. 18). This difference has been found to bear no relation to the phenomenon of maturation, since the chromosome count in the mature cells is the same, whether redia or cercaria is to be produced. In fact, it seems probable that the differentiation occurs before maturation. It is significant that the ova which develop into redia are comparatively simple while the ova which develop into cercariae are extremely complex. In this connection it has been observed that embryos developing from germ-balls produced from ova free in the body cavity produce daughter rediae. The maturing ova from the germinal epithelium lodged in the body wall of the parthenita develop either into rediae or cercariae. In his experiments on planarians Child (1915) has shown that starvation and fragmentation (fission) secure a rejuvenescence for the individual. The less differentiated individual is on the whole the younger one. From the present study on the life-history of trematodes there is justification for the belief that the undifferentiated eggs produce daughter parthenitae because they are simple, i.e., yoimger, while the more highly differentiated eggs grow into cercariae because they are physiologically old. Interpreted in this light, the parthenitic individuals of the Digenea are physiologically younger than the cercariae and the adult hermaphroditic forms because their structure is simpler. They have sacrificed complexity of structure to meet the needs of the parasitic life, and in so doing have become remarkably rejuvenated. In two species, Cercaria diaphana and C. micropharynx extreme simplicity has been assumed in the sporocyst, for the germ-balls develop from any cell of the body wall. The writer believes that the abihty of the parthenita to reproduce daughter rediae or sporocysts for two or more generations rests on the simplicity of the ovum and the relative simplicity of the parthenita, especially as regards the undifferentiated mesoderm cells. If this rejuvenation can be continued indefinitely, the parthenogenetic generations can also continue indefinitely without the intercalation of the hermaphroditic cycle. Child (1915:407) has stated that "in many cases parthenogenetic eggs are apparently less highly differentiated morphologically, and younger phy- siologically, than zygogenic eggs of the same species." The present study makes it necessary to add that in cases where the parthenogenetic eggs may develop into parthenitae or cercariae, the eggs which develop into the former 94 ILLINOIS BIOLOGICAL MONOGRAPHS [94 individuals are apparently less highly differentiated morphologically and younger physiologically than those which develop into cercariae. Finally the present study causes the writer to support the \'iew that the hermaphroditic phase of the life cycle of the Digenea is more closely related to the ancestral group than the parthenita, and that the simplicity of the parthenita has been assumed secondarily. This conclusion is based on the evidence that the original type was a highly complex Platyhelminth with ciliary integimient and eye-spots, characters found only in the miracidium. The modification of the parthenita has come about as the direct result of parasitism. It has lost its mesenchymatous matrix, its excretory tract has been extraordinarily modified, and its germ cells have become uniquely sim- ple. The nervous system of the redia has been simplified while the sporocySt lacks a nervous system entirely. In the sporocyst even the muscle cells have remained undifferentiated. Thus complexity in the hermaphroditic genera- tion of Digenea is an index of the unmodified condition of the group most early related to the prototype. SUMMARY 1. Trematode infection of mollusks of the Bitter Root Valley, Montana, is heavy. 2. The history of the germ cells of the sporoc}'^st and redia show them to arise parthenogenetically. 3. Parthenitae and adult hermaphoditic trematodes are comparable in- dividuals: likewise their germ cells can be referred to a common type of ger- minal epithehum. 4. The integimient of trematodes is mesodermal in origin. 5. The fundamental systems of the adult hermaphroditic trematode are well developed in the cercaria. 6. The excretory, genital and nervous systems of the cercaria may be used to show the natural relationships of the larvae. 7. Holostomes, like dis tomes, monostomes and amphis tomes, have an al- ternation of hermaphroditic and parthenogenetic generations. 8. Holostomes are probably of distome origin. 9. Parthenitae are well adapted to their parasitic life because their struc- ture is simple, in consequence of which they have become physiologically young. 95] LIFE HISTORY OF TREMATODES— FAUST 95 SPECIES DESCRIBED IN THIS PAPER. MONOSTOMATA Cercaria pellucida Faust 1917 Cer carta konadensis Faust 1917 HOLOSTOMATA Cercaria flabelliformis Faust 1917 Tetracotyle pipientis nov. spec. Cercaria ptychockeilus Faust 1917 DiSTOMATA Xiphidiocercariae Cercaria crenata Faust 1917 Cercaria glandulosa Faust 1917 Cercaria diaphana Faust 1917 Cercaria dendritica Faust 1917 Cercaria micropharynx Faust 1917 Cercaria racemosa Faust 1917 Echinostome Cercariae Cercaria trisolenata Faust 1917 Cercaria biflexa Faust 1917 Furcocercariae Cercaria gracillima Faust 1917 Cercaria tuberistoma Faust 1917 96 ILUNOIS BIOLOGICAL MONOGRAPHS [96 BIBLIOGRAPHY ANDRft , J. 1910. Zur Morphologic des Nervensystems von Polj^tommn integerrimum Frocl. Zeit. wiss. Zool., 95:191-220; 13 textfigs. Balfoxtr, F. M. 1881. A Treatise on Comparative Embryology, vol. II. London, 655 pp. Barker, F. D., and Laughlin, J. W. 1911. A New Species of Trematode from the Muskrat, Ftier ziic/AtcK^. Trans. Amer. Micr. Soc, 30:261-274; 1 pi. Bettendorf, H. 1897. Ueber Mnsculatur und Sinneszellen der Trematoden. Zool. Jahrb., Anat., 10:307-357; 5 Taf. Blanchard, E. 1847. Recherches sur I'organization des vers. 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Brit. Med. Jour., 1916, 1:411. Leiper, R. T., and Atkinson, E. L. 1915. Observations on the Spread of Asiatic Schistosomiasis. Brit. Med. Jour., 1915, 1:201-203; 1 pi. Lejtenyi, Th. 1881. Ueber den Bau des Gastrodiscus polymastos Leuck. Abhandl. Senkenberg. naturf. Ges. Frankfurt, 12:125-146; 3 Taf. Leuckart, R. 1863. Die MenschUchen Parasiten. Leipzig. 766 pp. 1886. Die Parasiten der Menschen. 2 Aufl. 1, Trematodes. Leipzig u. Heidelb. 534 pp. Leydig, Fr. 1853. Helminthologische Notizen. Zeit. wiss. Zool., 4:382-384. Lindner, E. 1914. Ueber die Spermatogenese von Schistosomum haematobium Bilh. (Bilharzia haematobia Cobb.), mit besonderer Beriicksichtigung der Geschlechtschromosomen. Arch. ZeUforsch., 12:516-538; 2 Taf. LiNSTOW, O. 1877. Enthelminthologica. Arch. Naturgesch., (1)43:173-198; 3 Taf. Looss, A. 1885. BeitrSge zur Kenntnis der Trematoden. Zeit. wiss. Zool., 41:390-446; 1 Taf. 1892. Ueber Amphistomum subclavatum Rud. 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Parasitische Plattwiirmer. I. Trematodes. Siisswasserfauna Deutschlands Heft 17. Jena. 218 pp. LtTTZ, A. 1916. Observagoes sobre a evolucao do Schistosomum mansoni. Nota previa. Brazil Medico, 30:385-387. Mathews, A. P. 1915. Physiological Chemistry. New York. 1040 pp. MmoT, C. S. 1897. Cephalic Homologies. A Contribution to the Determination of the Ancestry of the Vertebrates. Amer. Nat., 31:927-943. MiYAERi, K. UND Suzuki, M. 1914. Der Zwischenwirt des Schistosomum japonicum Kat. Mitt. med. Fakult. Univ. Kyushu, Fukuoka. 1:187-197; 2 Taf. Montgomery, R. E. 1906, 1906a. Observations on Bilharziosis among Animals in India. Jour. Trop. Vet. Sci., (1) 1:1-32, (1) 2:1-37; 4 pi. MoNTiCELLi, Fr. Sav. 1892. Cotylogaster Michaelis nov. gen., nov. spec. Leuckart's Festschr., pp. 164-214; 2 Tav. 1914. Ricerche sulla Cercaria setifera di Joh. Mtiller. Ann. Mus. zool. Univ. Napoli, (4) 4:1-49; 5 Tav. MOULINlf , J. j. 1856. De la Reproduction chez les Trematodes Endoparasites. M6m. de I'lnst. Genevois, 3:1-280; 6 pi. NiTZSCH, Ch. L. 1807. Seltsame Lebens- und Todesart eines bisher unbekannten Wasserthierchens, KiUan, Georgia. 257-262; 281-286. Cited after Braun 1893. 1816. Beitrag zur Infusorien-kunde der Naturbeschreibung der Zerkarien und Bazil- larien. Neue Schrift. Nat. Ges. Halle (1) 3; 1 Taf. Reviewed in Isis, 1818:728 NORDMANN, A. V. 1832. Mikrographische BeitrSge. I. Berlin. 118 pp., 10 Taf. Odhner, T. 1907. Zur Anatomie der Didymozoen: ein getrenntgeschlechtlicher Trematode mit rudimentaren Hermaphroditismus. Zool. Studien TuUberg, 1907:309-342; 1 Taf. 1910. Gigantobilharzia acotylea, n.g., n.sp., ein mit den Bilharzien verwandter Blut- parasit von enormer Lange. Zool. Anz., 35:380-385; 5 Figs. 100 ILLINOIS BIOLOGICAL MONOGRAPHS IlOO 1911. Zum natiirlichen System der digenen Trematoden. 1. Zool. Anz,, 37:181-191. 1912. Zum natiirlichen System der digenen Trematoden. V. Zool. Anz., 41:54-71; 7 Figs. Pagenstecher, H. a. 1857. Trematodenlarven und Trematoden. Heidelb. 56 pp., 6 Taf. Parona, C, e Ariola, V. 1896. Bilharzia Kowalewskii n. sp. nel Larus melanocephalus. Boll. Mus. Zool. e Anat. Comp. Univ. Geneva, 45:1-3. POIRIER, J. 1886. Tr6matodes nouveaux ou peu connus. Bull. Soc. philomath. Paris. Seance du 28 Nov. 1885. 21 pp. 4 pi. Pratt, H. S. 1909. The Cuticula and Subcuticula of the Trematodes and Cestodes. Amer. Nat., 43:705-729; 12 Figs. Rettger, L. J. 1897. Some Additions to our Knowledge of the Anatomy and Embryology of the Holostomidae. Proc. Ind. Acad. Sci., 1896:224, 225. Reuss, H. 1903. Beobachtungen an der Sporocyst und Cercaria des Distomum duplicatum. Zeit. wiss. Zool., 74:458-477; 1 Taf. ROSSBACH, E. 1906. Beitrage zur Anatomie und Entwicklungsgeschichte der Redien. Zeit. wiss Zool., 84:361-445; 4 Taf. ROSSETER, T. B. 1909. On Holostomum excisum (Linstow, 1906) and the Development of the Tet- racotyliform Larva to a Holostomum sp. Jour. Quek. Micr. Club, (2) 10:385-392; 1 pi. RUDOLPHI, C. A. 1819. Entozoorum SjTiopsis. 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St. Petersbourg, (8) 30:1-127; 6 pi. Russian. 101] LIFE HISTORY OF TREMATODES— FAUST 101 Steenstrup, J. J. S. 1842. Ueber den Generationswechsel oder die Fortpflanzung und Entwicklung dutch abwechselnde Generationen. Copenh. 60 pp. Stiles, Ch. W., and Hassall, A. 1908. Index Catalog of Medical and Veterinary Zoology. Trematoda and Trematode Diseases. U. S. Hyg. Lab. Bull. 37. 401 pp. Surface, F. M. 1907. The Early Development of the Polyclad, Planocera inquilina. Proc. Acad. Nat. Sci. Phila., 59:514-559; 6 pi. Tennent, D. H. 1906. A Study of the Life History of Bucephalus haimaenus: a Parasite of the Oyster. Quart. Jour. Micr. Sci., n.s., 49:99-133; 2 pi. Thomas, A. P. 1883. Life History of the Liver Fluke. Quart. Jour. Micr. Sci., 23:99-133; 2 pi. Thoss, E. 1897. Ueber den Bau von Holostomum cucuUus nov. spec. Leipzig. 66 pp., 2 Taf. Ward, H. B. 1909. Fasciolopsis buskii, F. Rathouisi, and Related Species in China. Trans. Amer. Micr. Soc, 29:5-16; 2 pi. 1916. 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Anz., 44:385-396; 3 Figs. 102 ILLINOIS BIOLOGICAL MONGRAPHS [102 EXPLANATION OF PLATES Abbreviations ad anterior dorsalis nerve ne nerrve ending al anterior lateralis nerve np nervus palatinus as anterior sensory field nph pharyngealis nerve av anterior ventralis nerve ns subesophageal commissure b, be genital atrium nt nerve trunk bl bursa glands o ovum br cerebral ganglion od oviduct c, ce cecum on oral nerve ring ca caudal pocket op optic nerve cell ceg cercaria germ-ball ope optic cup eg caudal gland cells opn optic nerve cr cirrus pouch or oral sucker cs collar spines ot oot3^e d.dl salivary gland duct ov ovary dc dorsal commissure P phar>-nx die dorsolateral commissure pa parenchyma dp profundus of dorsalis nerve pb polar body ds superficialis of dorsalis nerve pc preacetabular commissure e epithelium pd posterior dorsalis nerve ee ectoderm pe preoral sense endings eg excretory granules Pg primitive genital pore eb evertible prepharynx Pgl locomotor pocket glands ep excretory pore Pl posterior lateralis nerve es esophagus po postacetabular commissure et excretory tube pv posterior ventralis nerve ev excretory vesicle pvc postero-ventrolateraJis commissure ex excretory tubule pvi postero-ventral intermedius nerve fe flame cell r rhabdocoel gut g genital pore, birth pore rm ramus muscularis of the lateralis nerve gb germ-ball rp ramus palpalis of the lateralis nerve gle cystogenous cell sg salivary gland cell i intermedius nerve sp acetabular spine igl digestive gland st stylet 1 longitudinal muscle cell t basement membrane Ic Laurer's canal te, t],2 testis le lateral eye tr transverse muscle fiber Ig localized germinal epithelium u uterus Ip posterior locomotor pocket V vagina k lateral suctorial groove vd vas deferens m myoblast ve vas ef ferens me median eye-spot vf vitelline follicles mp musculus preoralis vi vitelline duct n.ne nerve cell vs acetabulum The lines in figures 6, 26, 51, 146, 147 have a value of 0.5mm; in figures 5, 7, 13-17, 19-20, 27-29, 31-34, 36, 37, 44-46,54, 56, 57, 61, 68-75, 77, 82, 83, 89, 91,92,97-99, 101, 102, 104, 107, 108, 111-113, 118, 119, 121-133, 136, 138, 140, 141, 145, 150-154, a value of 0.01 mm; in all other figures, a value of 0.05 mm. 103] UFE HISTORY OF TREMATODES— FAUST 103 PLATE I 104 ILUNOIS BIOLOGICAL MONOGRAPHS (104 DESCRIPTION OF PLATE Figs. 1-3. — Cercaria pellucida; sketches of progressive stages of pigmentation; dorsal view, showing two lateral eye-sp>ots and one median spot. X 100. Fig. 4. — Cercaria pdlucida; dorsal view, somewhat contracted. X 100. Fig. 5. — Cercaria pdlucida; anterior tip, figuring details of pigmentation and contents of the excretory tube. X 330. Fig. 6. — Cercaria pellucida; redia,^characteriz€d by extensive rhabdocoel gut and spinous prepharynx. X 34. Fig. 7. — Cercaria pellucida; detail of the spinous prephar^Tix of the redia. X 540. Fig. 8. — Cercaria pdlucida; young redia; precocious development of the cercariae before the redia is mature. X 38. Figs. 9-11. — Cercaria pellucida; three stages in encystment. X 38. Fig. 12. — Young Cercaria pdlucida; origin of posterior locomotor pockets within the caudal pocket. X 170. Fig. 13. — Cercaria pellucida; transverse section thru the middle of the body. X 330. Fig. 14. — Cercaria pdlucida; detail of cystogenous gland cells in the region of the lateral eye- spot. X 330. Fig. 15.— Cercaria pdlucida; contracted excretory bladder and posterior locomotor pockets. X 238. Figs. 16, 17. — Cercaria pellucida; details of the posterior locomotor pocket; Fig. 16, con- tracted; Fig. 17, relaxed; xx, retractor muscles; yy, reflexor muscles. X 540. Fig. 18. — The genitalia of Cercaria pdlucida; r^ons of ootype and metraterm. X 238. Fig. 19. — Cercaria pellucida; transverse section thru tail, indicating arrangement of ordinary parenchyma cells. X 540. Fig. 19a. — Cercaria pdlucida; oblique section thru tail, indicating arrangement of muscle fibers. X 540. ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME 4 19 a FAUST LIFE HISTORY OF TREMATODES PLATE I 1051 UFE HISTORY OF TREMATODES— FAUST 105 PLATE II 105 ILLINOIS BIOLOGICAL MONOGRAPHS [106 DESCRIPTION OF PLATE Fig. 20. — Cercaria pellucida; sagittal section thru pharynx and gut of redia, with prepharynx organ retracted. X 330. Fig. 21. — Cercaria pellucida; transverse section thru body in region of posterior locomotor pocket glands. X 170. Fig. 22. — Cercaria pellucida; optical view of the proliferation of the germ-balls from the posterior germinal epithelium of the redia. X 330. Fig. 23. — Cercaria pellucida; central nervous system, typical for the trioculate species of monostome cercariae. X 330. Fig. 24. — ^Yoimg Cercaria pellucida; oblique section thru ganglion mass, sho';nng connection of eye-spots with brain center. X 330. Fig. 25. — Cercaria konadensis; dorsal view. X 105. Fig. 26. — Redia of Cercaria konadensis. X 34. Fig. 27. — Cercaria konadensis; detail of paired group of caudal gland cells. X 540. Fig. 28. — Cercaria konadensis; genital cell masses in region of ootype. X 540. Fig. 29. — Cercaria konadensis; detail of excretory bladder and posterior locomotor pockets. X 238. Fig. 30. — Cercaria konadensis; optical view of the germinal rachis of the redia. X 330. Fig. 31. — Cercaria konadensis; sagittal section thru aspinose prepharynx of the redia. X 330. Fig. 32. — Mature Cercaria urbanensis Cort; transverse section thru tail, showing caudal gland cells. X 330. Figs. 33, 34. — Cercaria urbanensis; stages in differentiation of caudal gland cells from ordinary parenchyma cells. X 330. Fig. 35. — Cercaria urbanensis; detail of excretor>' vesicle and posterior locomotor pockets. X 238. Fig. 36. — Early germ-balls of Cercar /a «rJa»e«5J5; oblique section thru brain mass and lateral eye-spot, showing ectodermal origin of pigment cup, and connection with optic cells of brain. X 730. Fig. 37. — Oblique longitudinal section thru Cercaria pellucida, showing detail of nerve endings. X 730. ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME 4 FAUST LIFE HISTORY OF TREMATODES PLATE II [107 LIFE HISTORY OF TREMATODES— FAUST 107 PLATE III 108 ILUNOIS BIOLOGICAL MONOGRAPHS [108 DESCRIPTION OF PLATE Fig. 38. — Cercaria fldbdliformis; ventral view of worm freed from cyst; U, lateral lappets X 80. Fig. 39. — Cercaria flabelliformis; dorsal view, giving details of the excretory system and genitalia. X 80. Fig. 40. — Cercaria flabelliformis; lateral view, showing suctorial cup in anterior portion of worm; U, lateral lappets. X 80. Fig. 41. — Immature Cercaria flabelliformis within cj'st. X 54. Fig. 42. — Cercaria flabelliformis; yoimg redia, detailing the excretory chaimels in the worm. X 54. Fig. 43. — Cercaria flabelliformis; redia showing paired salivary glands emptying into the oral pocket. X 54. Fig. 44. — Cercaria flabelliformis; mid-frontal section thru young daughter redia in region of germinal cell maturation. X 330. Fig. 45. — Cercaria flabelliformis; median frontal section thru yoimg daughter redia, showing proliferation of germinal epithelium at posterior end of gut. X 330. Fig. 46 a-m. — Cercaria flabelliformis rediae; matiu-ation of parthenogenetic ova; A, resting cell; B, C, formation of spireme; D, division of spireme skein into eight chromosomes; E. P, G, longitudinal splitting of chromosomes at equatorial plate; H, mitosis, with forma. tion of polar body and preparation of ovum for second mitosis; /, polar body almost constricted off, chromosome b excentric; /, ovum preparing for second division, polar body also dividing; K, cell cleavage, with precocious chromosomes bi, b2 excentric; L, first cleavage of a cercaria-ov\mi, with polar body degenerating; M, metaphase of a somatic cell in process of division. X 1620. ILLINOIS BIOLOGICAL MONOGRAPHS VOLUMES FAUST LIFE HISTORY OF TREMATODES 1091 LIFE HISTORY OF T REM ATODES— FAUST 109 PLATE IV no ILLINOIS BIOLOGICAL MONOGRAPHS [110 DESCRIPTION OF PLATE Fig. 47. — Tetracotyle pipientis; ventral view, showing digestive tract and genital system. X 105. Fig. 48. — Tetracotyle pipientis; diagram of the excretory system, with excretory granular inclusions. X 105. Fig. 49. — Cercaria ptychocheilus; ventral view, including digestive, excretory and genital systems. X 105. Fig. 50. — Cercaria ptychocheilus; sketch of encysted worm. X 25. Fig. 51. — Cercaria ptychocheilus; sketch of ruptured cyst with attachment annulus. X 25. Fig. 52. — Cercaria ptychocheilus; detail of genital system. X 165. Fig. 53. — Cercaria ptychocheilus; nervous system. X 330. Fig. 54. — Cercaria ptychocheilus; transverse section thru middle of body. X 540. Fig. 55. — Cercaria crenata; dorsal view. X 170. Figs. 56, 57. — Cercaria crenata; ventral and lateral views of stylet. X 540. Fig. 58. — Cercaria crenata; sporocyst. X 54. Fig. 59. — Cercaria crenata; detail of genitalia. X 170. Fig. 60. — Cercaria glandulosa; ventral view. X 370. Fig. 61. — Cercaria glandulosa; ventral view of stylet. X 370. Fig. 62. — Cercaria glandulosa; salivary and cystogenous glands. X 75. Fig. 63. — Cercaria glandulosa; detail of caudal pockets, showing insertion of tail, spinose lateral grooves, and three-spined ventral flap. X 100. Figs. 64, 65. — Cercaria glandtilosa; outline of excretory vesicle, open and closed. X 200. Fig. 66. — Cercaria glandulosa; genital cell masses, dorsal view. X 110. Fig. 67. — Cercaria glandulosa; sporocyst. X 170. ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME 4 FAUST LIFE HISTORY OF TREMATODES PLATE IV Ill] UFE HISTORY OF TREMATODES— FAUST 111 PLATE V 112 ILLINOIS BIOLOGICAL MONOGRAPHS [112 DESCRIPTION OF PLATE Figs. 68-70. — Cercaria glandnlosa; consecutive frontal sections, giving details of the nervous system anterior to the brain. X 540. Fig. 71. — Cercaria glandtdosa; frontal section, with details of innervation of acetabulum. X540. Fig. 72-75. — Cercaria glandulosa; transverse sections thru levels aa to dd oi Fig. 60. X 540. Fig. 76. — Cercaria diaphana; ventral view, considerably flattened by cover slip. X 170. Fig. 77. — Cercaria diaphana; ventral view of stylet. X 540. Fig. 78. — Cercaria diaphana; ventral view, giving details of glands and genital cell masses. X 170. Figs. 79, 80. — Cercaria diaphana; sporocysts. X 80. Fig. 81. — Cercaria dendritica; ventral view. X 170. Figs. 82, 83. — Cercaria dendritica; lateral and ventral views of stylet. X 250. Fig. 84. — Cercaria dendritica; encysted worm. X 150. Fig. 85. — Cercaria dendritica; salivary and cystogenous glands. X 170. Fig. 86. — Cercaria dendritica; genital system. X 150. Fig. 87. — Cercaria dendritica; yoimg sporocyst. X 150. Fig. 88. — Cercaria dendritica; mature sporocyst. X 150. Fig. 89. — Cercaria dendritica; posterior end of mature sporocyst, showing origin of germ- balls from localized germinal epithelium. X 330. ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME 4 FAUST LIFE HISTORY OF TREMATODES PLATE V 113] LIFE HISTORY OF TREMATODES— FAUST 113 PLATE VI 114 ILLINOIS BIOLOGICAL MONOGRAPHS [114 DESCRIPTION OF PLATE Fig. 90. — Cercaria micro pharynx; ventral view. X 170. Figs. 91, 92. — Cercaria micropharynx; ventral and lateral views of stylet. X 540. Fig. 93. — Cercaria micropharynx; distribution of glands. X 170. Fig. 94. — Cercaria micropharynx; sporocyst with non-localized germinal epithelium. X Fig. 95. — Cercaria micropharynx; cercariae encysted in old sporocyst. X 54. Fig. 96. — Cercaria micropharynx; genital cell masses. X 170. Fig. 97. — Cercaria micropharynx; transverse section thru brain center. X 540. Fig. 98. — Cercaria micropharynx; transverse section thru excretory comua. X 540. Fig. 99. — Cercaria micropharynx; transverse section thru tail. X 540. Fig. 100. — Cercaria racemosa; ventral view. X 150. Figs. 101, 102. — Cercaria racemosa; ventral and lateral views of stylet. X 330. Fig. 103. — Cercaria racemosa; detail of salivary glands. X 150. Fig. 104. — Cercaria racemosa; genital cell masses. X 330. Figs. 105, 106. — Cercaria racemosa; sporocysts, showing localized germinal epithelium and attachment organ, ao. X 54. Fig. 107. — Cercaria racemosa; lateral view of genital cell masses in region of acetabulum. X 330. Fig. 108. — Cercaria racemosa; optical view of the sporocyst in region of birth-pore, bp; arrow points toward attachment organ. X 330. Fig. 109. — Cercaria trisolenata; ventral view. X 150. Fig. 110. — Cercaria trisolenata; dorsal view of collar spines. X 170. Fig. 111. — Cercaria trisolenata; lateral view of collar spines. X 330. Fig. 112. — Cercaria trisolenata; sketch of acetabular spines. X 540. Fig. 113. — Cercaria trisolenata; typical cystogenous cell glands, showing granules and chro- midia. X 540. Fig. 114.4-E. — Cercaria trisolenata; sketches of developmental stages. X 80. Fig. 115 A-C. — Cercaria trisolenata; stages in encystment. X 80. ILLINOIS BIOLOGICAL MONOGRAPHS -st VOLUME 4 LIFE HISTORY OF TREMATODES PLATE VI 1151 LIFE HISTORY OF TREMATODES— FAUST 115 PLATE VII 116 ILLINOIS BIOLOGICAL MONOGRAPHS [116 DESCRIPTION OF PLATE Fig. 116. — Cercaria trisolenata; encysted worm. X 150. Fig. 117. — Cercaria trisolenata; redia. X 50. Fig. 118. — Cercaria trisolenata; longitudinal and transverse muscle fibers of the digestive tract, showing myoblast connections. X 730. Fig. 119. — Cercaria trisolenata; peripheral muscle fibers of longitudinal system. X 730. Fig. 120. — Cercaria trisolenata; genital cell masses. X 220. Fig. 121. — Cercaria trisoleruUa; butterfly stage in development of the central nervous system. X 330. Fig. 122. — Cercaria trisolenata; differentiating stage in development of central nervous system. X 330. Figs. 123, 124. — Cercaria trisolenata; lateral and dorsal views of central nervous system of mature cercaria. X 330. Fig. 125. — Cercaria trisolenata; central nervous system of the redia. X 220. Fig. 126. — Cercaria trisolenata; distribution of nerve cells in the redia, median sagittal sec- tion. X 330. Fig. 127. — Cercaria trisdenata; detail of the peripheral nerves of the redia. X 540. Figs. 128-133. — Cercaria trisolenata; traiisveTst sections at levels aatofol Fig. 109. X 330. ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME 4 LIFE HISTORY OF TREMATODES PLATE VII 117] UFE HISTORY OF TREMATODES— FAUST 117 PLATE VIII 118 ILLINOIS BIOLOGICAL MONOGRAPHS [118 DESCRIPTION OF PLATE Fig. 134. — Cercaria biflexa; ventral view, showing salivary gland cells. X 105. Fig. 135. — Cercaria biflexa: ventral view, showing excretory system. X 105. Fig. 136. — Cercaria biflexa; lateral view of collar spines. X 330. Fig. 137. — Cercaria biflexa; redia of worm. X 170. Fig. 138. — Cercaria biflexa; detail of three flame cells in cephalic region. X 540. Fig. 139. — Cercaria biflexa; genital cell masses. X 170. Fig. 140. — Cercaria trisolenata; posterior end of redia. X 540. Fig, 141. — Cercaria biflexa; posterior end of redia. X 540. Fig. 142. — Cercaria gracillima; ventral view. X 230. Fig. 143.— Cercaria gracillima; excretory system. X 350. Fig. 144. — Cercaria gracillima; dorsal view of trunk, showing eye-spots and salivary glands X 350. Fig. 145. — Cercaria gracillima; detail of flame cell of excretory system. X 750. Figs. 146, 147. — Cercaria gracillima; sporocysts; Fig. 146, x 14; Fig. 147, X 21. Fig. 148 A-G. — Cercaria gracillima; stages in development. X SO. ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME 4 FAUST LIFE HISTORY OF TREMATODES PLATE VIII 119] UFE HISTORY OF TREMATODES— FAUST 119 PLATE IX 120 ILLINOIS BIOLOGICAL MONOGRAPHS [120 DESCRIPTION OF PLATE Fig. 149. — Cercaria graciUima; genital cell masses. X 270. Fig. 150. — Cercaria graciUima; nervoiis system. X 540. Fig. 151. — Cercaria graciUima; central nervous system in a very yoimg germ-ball. X 540. Fig. 152. — Cercaria graciUima; transverse section thru esophagus glands. X 540. Fig. 153. — Cercaria graciUima; transverse section thru region slightly posterior to that shown in Fig. 152. X 540. Fig. 154. — Cercaria graciUima; transverse section thru salivary glands. X 540. Fig. 155. — Cercaria tuberisloma; ventral view. X 170. Fig. 156 A-F. — Cercaria tuberisloma; stages in development. X 75. Figs. 157, 158. — Cercaria tuberisloma; sporocysts. X 54. Fig. 159. — Cercaria biflexa; section thru liver tissue of Physa gyrina Say, showing infection; a, disintegrating cecvmi; b, broken down connective tissue; c, section of worm. X 170. Fig. 160. — Cercaria micropharynx; section thru liver tissue of Lymnaea proxima Lea, infected with the worm; a, fatty bodies in degenerating cecimi; b, vacuoles; c, sloughing tissue; d, karyolysis; e, section of worm. X 170. Fig. 161. — Cercaria graciUima; section thru liver tissue of Physa gyrina Say infected with the worm; a, cytolysis; b, fatty globules; c, karyolysis; d, vacuoles; e, fibromata;/, sand inclusions; g, section of worm. X 240. ILLINOIS BIOLOGICAL MONOGRAPHS VOLUME 4 FAUST LIFE HISTORY OF TREMATODES PLATE IX i