(JB^wv^- Ko^2Gs*^3- K0BENHAVN HOVEDKOMMISSION.ER: ANDR. FRED. H0ST & S0N, KGL. HOF-BOGHANDEL BIANCO LUNOS BOGTRYKKERI 1920—21 ^HSOA^ C I DEC 12 1958 Preface. x he history of the work which I hereby take the liberty to offer to the scientific world has been rather peculiar. More than twenty years ago I saw that our temporary forest ponds which got water in November — December very often, a few days later, contained living mosquito larvae; I saw that these larva; hibernated under the ice and that they could be found again when the ice melted in the spring. To me it was rather an astonishing fact to find in 1900 air-breathing insect larva? below the ice, locked out by the ice from the atmospherical air. In the following years I often visited the temporary ponds in spring and ascertained that they teemed with mosquito larvae. Even the slightest study with a magnifying glass showed that these larvae differed very much from the hibernating larvae. In the admirable chapter in "Histoire des insects" Reaumur has shown that Culex pipiens hibernates as imago and lays its eggs in batches, eggboats. In his work "History of Aquatic Insects" Miall has had nothing to add; as far as I know, Reaumur's exposition of the biology of C. pipiens has for more than a century been used as a model of the development of all mosquitoes. In accordance with this fact year after year I searched for the eggboats in the temporary ponds of our forests; I never saw a single one. In the following years I slowly came to understand that there was also upon another point a striking discrepancy between what we have learned and what I found out on studying Nature herself. Scientists as well as ordinary people have all been inclined to suppose that a great number of generations are hatched during the year. Without any more thorough exploration I felt sure that most of the mos- quitoes really had only one single generation. In the spring of 1905 I tried to hatch the above-named two mosquitoes, the one with the hibernating larvae, and the one with the larva5 which only appeared after the ice had melted; the former larva had very large antenna? and a long sipho; the latter very small antenna1 and a very short sipho; of course I got two species of mosquitoes; but the one with the hibernating larva was unquestionably new to our fauna. Having however taken material from different forest ponds, to my astonishment I saw that those mosqui- toes which derived from the hibernating larva' always gave the same species, whereas those deriving from the larva? in spring, gave specimens which unquestion- ably belonged to two or three different species. I now understood that here was a very wide field for further exploration; as. however a long series of papers: my plancton work, many papers relating to the biology of freshwater insects, and the bathymetrical explorations of the Fureso- district first had to be carried out, I could only at rare intervals get time for these observations during the 10 years from 1905 to 1915. Still the mosquito studies were not quite laid aside, and in 1916 a more thorough study of the mosquito larvae and their biology began. In 1912 the first volume of the great work of Howard, Dyar and Knab relating to the mosquitoes of North and Central-America appeared; the volume did not reach me before 1916. I immediately saw that all my above- named more cursory conjectures were indeed correct, but also, that if published they could not be regarded with any really new interest. In the time from 1910 — 1920 a series of shorter papers, dealing with the biology of the European species, appeared, and the biological facts, mentioned by the American authors, were generally corroborated by the European ones. In my opinion this literature very often by no means comes up to the standard which should be exacted for scientific work. After brief reflection I resolved that I would carry to an end my own studies in spite of the whole American and European literature, and moreover that during the study I would not take the slightest notice of it. My leading scientific views were the following. From a purely scientific point of view, I have always regarded the question, who first made a biological observation as a matter of sublime indifference. It must never be forgotten, that even with regard to biological observations which can only rarely be committed to paper with the same convincing exactness as an anatomical structure, the exact apprehension of a given fact can only be acquired through repeated observation. It is further of the greatest significance that the biological observations are tested by different scientists and in different latitudes; only in that way can our suppositions and hypotheses be registered among real scientific facts. It must further be remembered that the study of Nature must always begin with the slightest possible literary ballast. He who has first crammed his head with all that has been written upon a subject, will at the moment of observa- tion, when standing face to face with Nature, soon understand that his whole learning is only felt as a burden and restricts his power of observation. I for my own part have always been of the opinion that it is exactly the smallest equipment of human knowledge which gives the greatest peace in my studies, creates the scientific sovereignty over observations and thoughts and — as far as possible — moves the milestones of time nearer to the borders of eternity. Having used the neighbourhood round Hillerod for more than twenty-five years for my studies relating to the freshwater organisms, and often visiting the hundreds of temporary ponds which were scattered within a radius of about 7 kilom. over the country, especially in the forest, I had a rather extensive knowledge of these ponds; having often hatched larva material from many of these ponds, I knew well which would give the best results, if more thoroughly studied. In accor- dance with this knowledge twenty-five temporary forest ponds were selected, and in the time 1916 — 1919 subjected to a regular fortnightly exploration. After the establishment of the Freshwater Biological Laboratory at Tjustrup lake, near Soro, in the middle of Seeland, I soon found 15 other ponds, mainly belonging to the open meadows and large plains which were simultaneously included in the exploration. The ponds were explored every fortnight, viz. during the winter, when the ponds were frozen and covered with snow, at longer intervals, but in spring, when the different larva? appeared, and the imagines arrived, as often as possible, i. e. many of them almost every day. The ponds were so selected that in the course of a single excursion I could reach from five to seven. On schemata the results of every excursion were noted and observations with regard to the freezing and drying periods taken down. At first I took the temperature of the ponds, but later on I learned that this was quite useless; on sunny days the temperature might be about thirty degrees Celsius, the next day, if the weather was cold and rainy, only about ten. The temperatures could only acquire, scientific significance if I had been able to indicate the total sum of heat-units which in the course of the year was conveyed to the ponds. As this was impossible, the temperatures were not regularly taken. In 1916 I thought that I should only find very few mosquitoes in the diffe- rent ponds; in Denmark we had hitherto, viz: St.eger in his valuable old work: Systematisk Fortegnelse over de i Danmark hidtil fundne Diptera, only found ten species of Culicini and of these two were doubtful (C. annulipes Meig. and C. nigripes Zett.) and one restricted to brackish water; the greatest number that I could ex- pect to find, in my area of distribution, was therefore only seven. At that time I had not the slightest idea that the determination would cause troublesome diffi- culties. I supposed that I could only expect to clear up the biology of the well known species: C. nemorosus Meig., cantans Meig., orncttus Meig., pipiens Linne and annulatus Schrank; further I did not know that the larvae of these species practi- cally speaking were quite unknown, or at all events insufficiently described; the valuable work of Meinert: De eucephale Myggelarver 1886, deals only slightly with the larva1 of Culicini. Already in 1916 I understood that this number would be augmented with several new species, but the determination of these species was quite impossible to me. A closer examination of the large larva material from the many ponds, worked out in the winter months, showed that there were especially some ponds, which must be examined with special care next year. In 1917 these ponds were examined almost weekly from lf> April to the first part of July. In this time I then saw from five to seven species appear and disappear after each other. Some of them were detected in the larva stage, separated in this stage, and then hatched in special vessels; others appeared from larva material which I lirst thought was homogeneous. In 1917 I had demonstrated about 1,") different species, and in 1918 I tried to elucidate the biology of all these species. To my great satis- faction I saw that I almost always might be sure that the different species year after year were hatched in the same ponds and almost always at the same tempera- ture. As the larva? appeared in the ponds, they were separated, and about a hun- dred placed in a special vessel and the vessel set in a hatching cage. The skins were preserved and where I got a quite homogeneous imago material from a vessel, I was sure that I had the right connection between larva and imago. In 1919 many doubtful questions were tried and tried again; and several of them were now nearer to being solved; especially the group 0. nemorosus, was ex- tremely troublesome. Again and again I came to the conclusion that there are species which may easily be distinguished in the imago stage, but which as larvae cannot be distinguished from each other; further that there are species which as larva? may be distinguished at a first glance, but as imagines are almost indistinguishable. At this time the final determination of the species was desirable; most of them at that time had only numbers. Having myself tried to determine the material, I saw, that if I used the ordinary works on the European mosquitoes for some of the most characteristic species, this gave no result. I then reguested my friend Prof. Simon Bengtson of Lund to compare some of my material with Zetterstedt's speci- mens in Lund; as I however compared the determinations with my larva material I saw that somewhere there must be some mistake. I then sent some of the most troublesome species to Mr. Edwards at the British Museum and asked him to look them over. From him I got the wholly unexpected result that, in my material, there were no less than three American species: 0. abfichii (Felt), fletcheri (Coquil- let) and diantceus (H. D. K.), which have hitherto not been found in Europe; in a following collection Mr. Edwards then determined a fourth species 0. prodotes (Dyar), which also hitherto was only found in America; this species I had over- looked; having examined the preserved larva material from the pond in which this species should have been hatched, I really found a very few highly charac- teristic larva? which most probably belonged to this species. Next year these larva? were found again in the same pond, separated and, when hatched, really gave 0. prodotes. Later on it was found out by Mr. Edwards that 0. fletcheri was identic with 0. lutescens (F.) and 0. abfichii with 0. excrucians Wlk. Mr. Edwards further came to the same conclusion as I, that the old species C. ornatus Meig. could not be found in my material; those determined by St.eger and now in the collection of the Boyal Museum, Copenhagen, being partly Culicella morsitans, partly C. com- munis. As these species, apart from 0. prodotes, which was studied in 1920, were separated as numbers already in 1918 and with regard to all biological data proto- colled separately, it will be understood that with regard to the biology of the species, it was not of the slightest significance that they were not finally determined till 1919. In 1920 two questions had to be solved before the work could be finished. As the two freshwater laboratories in Hillerod and at Tjustrup were both situated far from the sea-shore, I had no opportunity to study the sea-shore mosquito fauna, where the habitat of 0. dorsalis Meig., already found by Staeger, really is. It might further be expected, that here also we might find two other species 0. curriei (Coquillet) an American species, already found in England, and 0. detritus (Haliday). Both species were found. As almost all my studies hitherto had been restricted to Seeland, with some small trips to the southern islands, it was of in- terest to become acquainted with the mosquito fauna of Jutland. My time now being occupied with the preparation of the work for print, I requested Mr. Kryger, whom I know as a very skilled observer, to follow the develop- ment of the mosquito life in the brackish-water pools near Copenhagen, and on a journey in Jutland to study mosquito life there. Mr. Kryger was also to gather information with regard to the occurrence of Anopheles in stables. Staeger indicates 15 Culicida?, of which one C. nigripes must unquestionably be cancelled. Thirteen new species have now been found for our fauna, this now consisting of twenty-five species. The new species are: Ochlerotatus curriei (Coquillet), 0. lutescens (F.), 0. excrucians (YVTk.), 0. detritus (Haliday), 0. punctor (Kirby), 0. prodotes (Dyar), 0. rusticus (Rossi), 0. diantcvus (Howard, Dyar and Knab), 0. sticticus (Meig.), Tceniorynchus Richardii (Ficalbi), Culicella morsitans (Theobald), Culex ciliaris Linne, C. nigritulus Zetterstedt. Three of the species were new for Europe. Of these thirteen species I have myself found the twelve; 0. stic- ticus has been brought me by Mr. Kryger from the western part of Jutland. Of the twenty-five species the twenty have been hatched from larva-. Most of these larvse have hitherto only been very badly described or were wholly unknown. It will of course be understood that the exploration has taken much more time than I had thought, when I began. To a much higher degree than I had first thought the work had to be systematic. Gradually I understood that a redescrip- tion of the American species was necessary, that all the species of the nemorosus- communis group should be redescribed, and that all the larva? had to be described and carefully delineated. It was very much against my wishes that I was forced into scientific work to which I have always been a stranger. I soon learned that my descriptions of the imagines would be best if I followed the descriptions by Howard, Dyar and Knar as closely as possible. Everywhere where it has been possible I have therefore followed the descriptions of imagines by these authors. Reference only to the work of Howard, Dyar and Knar was not possible, be- cause slighter differences could almost always be detected. With regard to the description of larvae the case is different; these are always wholly original, and it will be understood that new characters have been used and the older ones esti- mated in a way differing from that of earlier authors. As stated above: What I had intended should be the main points of the work: the statements that almost all our mosquitoes only possess one single generation, and that the eggs of the Aedini are laid singly and not in eggboats, have now been made by others. Now one of the main results of the exploration, a result which was not intended, when the exploration began, is probably, that the North- and Cen- tral-European mosquitoes should now be recognisable in the larva and imago stage; 8 in the pupa stage I do not think that they are so. I first intended in two exten- sive chapters to give biological sketches of each of the forty ponds, and of the neighbourhood where some of the more peculiar species are found; further to print the large schemes of each of the forty ponds, carried on for almost four years; the schemes show how each of the species appears and disappears in the course of the year. Especially these schemes were extremely expensive to print, and I suppose that their real scientific value is but slight; they may be regarded as rough draughts, and will not be printed owing to the great expense. — With regard to the synonyms I have only given the most necessary information; 1 refer to the work of Lang (1920) and to others which I know are under preparation. As it will be understood from the foregoing pages, this work stands in the greatest debt to Mr. Edwards of the British Museum ; I hereby express my most cordial thanks for all the help he has furnished me with; further to Prof. Simon Bengtson and, last but not least, to Mr. Kryger who with great skill and warm interest has solved the tasks, I have given him. A few months before this work was sent to press, Mr. Lang's valuable work, relating to the British mosquitoes, appeared; more than any other it has shown that my paper, now published, issuing from quite different stand-points, and worked out on other principles, is by no means superfluous. Also the Caresbergfund I bring my heartiest thanks for two sums, by means of which I was able to explore the southern islands, mainly with regard to the Anophilines. For the study of the living larvae the excellent bino- culary aquarium microscope, also presented to me by the Carlsbergfund, has been of the greatest value. All the tables are drawn by myself and all figures of the same kind are drawn with the same power and all with camera. Key to the tables: 1 head (Leitz Ob. 3 Oc. 1) 2 antenna (Leitz Ob. 3 Oc. 6) 3 mandible (Leitz Ob. 3 Oc. 6) 4 maxilla (Leitz Ob. 3 Oc. fi) 5 mentum (Leitz Ob. 6 Oc. 1) (i the last segments (Leitz Ob. 3 Oc. 1) 7 scales in comb (Zeiss horn. im. Oc. 6) 8 pecten (Zeiss Ob. B Oc. 6) 9 single thorns in pecten (Leitz (5 Oc. 6). The Freshwater Biological Laboratory. Hillerad. '%> 1920. I. Culicines. Chapter I. Morphological Remarks. a. The Larva. In the following pages I have tried to elucidate some points in the anatomy of the Culicin larvse and as far as possible compared the anatomical structures with the use the larva makes of them. The chapter deals only with our Danish mos- quito fauna; it would certainly be desirable if the contents could be based upon larva material gathered in other regions of the world. In the terminology I have followed the excellent work of Howard, Dyar and Knab. The Head of a mosquito larva is generally wider than it is long, rarely almost isodiametric as in Finlaya geniculata; it may be rectangular as in Tamiorynchus; it is commonly vaulted, but may be flattened (Tivniorynchus) or, as in some of the species of the genus Ochlerotatus, semiglobular. The anterior margin is formed by a narrow clypeus furnished with two stout spines, between which the labrum is attached. The greater part of the upper surface of the head carapace is occupied by the front or epistome. It bears a number of seta1, the number and arrangement of which are of significance for classification (Knab 1904 p. 175). Apart from some small tufts, the epi- stome almost always bears three pairs of tufts, the preantennal tufts, at the root of the antenna?, provided with many and often long hairs; only in Finlaya there are three; the two other pairs are either arranged in an arch over the epistome or they are arranged on two lines anterior posteriorly. They are then described as lower and upper frontal tufts. These tufts are rarely multiple in the Danish species. The number of hairs is greatest in the genus Culicella (five or six) Cule.r, Theobaldia and Aedes. In the genus Ochlerotatus the number is commonly only from four to One. The hair formula: two strong hairs in lower frontal tuft and four in the upper, is characteristic of the group 0. excrucians, cantans, lutescens, annulipes. In 0. diantceus the arrangement of hair-tufts and their number of hairs are more in accordance with that of the genus Culicella. There is always most hairs in the upper frontal tuft; the highest number I have found, is six (C. morsitans) in Theobaldia annulata commonly four. The lower frontal tufts have generally three or two, but these hairs are stronger than those of the upper D. K. D. Vidensk. Selsk Skr , naturvidensk. i>n matheni. Afd. 8. Rrckke, VII, 1. 2 10 frontal tufts. In some species, 0. prodotes and caspius, the number of hairs in both tufts is restricted to one single long hair; Finlaya geniculata has two in the upper and one single hair in the lower frontal tuft. In Tceniorhynchus Richardi the upper fron- tal tuft is lacking; in T. annulata we find an additional lateral, strong, tuft in the notch between eyes and antenna. Often and especially in Tceniorhynchus we find small multiple tufts between the above-named larger ones; these tufts are not marked because they are rather inconstant. The epistome has often drawings, different among the different species, but remarkably constant in the same. I refer especi- ally to the tables of T. annulata, 0. rusticus a. o. The colour of the epistome is com- monly either grey or yellowish red. When in spring the drying ponds in our woodlands teem with the large, grey larvae of 0. communis, prodotes a. o., ready to pupate, we almost always find, scattered in the swarms, many, smaller larva? diffe- ring by their yellowish red heads from these larva?; these larvae with red heads belong to 0. cantons which will shortly, when the others have disappeared, pre- dominate in the ponds. The mosquito larva? have commonly two pairs of compound lateral eyes, ocelli, like those of other aquatic insect larva?, being absent; in the Tceniorhynchus larva?, living at the bottom of the ponds, between the roots and almost in total darkness, we find only a single pair of very small eyes. The outer form of the two pair of lateral eyes is different in the different stages of the larva?; in the same species they are often almost separated by a narrow band; the posterior pair has as a rule not been marked in the figures. The Antenna? consist of a single piece; they are remarkably stiff and possess only very slight mobility; their length differs greatly, commonly they are half as long but often as long as the head; in F. geniculata they are extremely short, only one fourth of the length of the head; in some species, as C. pipiens and C. nigritulus, they are longer than the head, and in Culicella morsitans and Tceniorhynchus Richardi more than three times longer. In the short antennated species the antenna? are almost straight, only slightly curved. Where the antenna? are very long, they are especially, as in C. morsitans, elegantly curved, forming together two large, down- ward directed arches before the head. The antenna? always taper at the apex and in the middle of the shaft or about two-thirds from the base of the shaft, often, in a constricted part of the antenna, is inserted a fan-shaped tuft of long, commonly feathered hairs. In Ochlerotatus, Theobaldia and Aedes cinereus they are inserted directly on the antenna, in Culicella on a conspicuous notch. The development of the tuft is very various; in Finlaya geniculata it consists of only one single un- feathered hair; commonly, as in most species of the gen. Ochlerotatus it has only from five to seven hairs; but in Culex pipiens, C. nigritulus, Culicella morsitans, 0. diantcvus and Tceniorhynchus the number is from twenty to thirty; here too, the single hairs are very long, forming in these species two large wheels with feathered spokes. When the larva is hanging from the surface or from a plant, the tuft is always folded out; a movement of the single rays is rarely observed, but I have 11 often seen the whole wheel suddenly thrown inwards or vice versa. The part of the antenna from tuft to apex is almost always narrower than that from tuft to base; generally it is stiff, but in Tceniorhynchus it is modified into a very long, extremely flexible flagellum, bearing a single bristle near the tuft, but ending without any hairs at the apex. — The outer part of the antenna is almost always (except F. r/eniculata) of a much darker colour than the inner part. In C. morsi- tans the inner part is of an elegant ivory-white shining colour, strongly contrasting with the almost black outer part. At the apex the antenna carries a different number of shorter or longer hairs, two of which are as a rule inserted a little from the apex, the others at the apex itself; the latter further carries one or two digit-shaped soft organs, undoubtedly of sensory function. When we remember that all our Culicin larvae are almost of the same size, and only a few of them half as long as the largest, further, that the larva of F. geniculata, almost of the same size as C. morsitans, has antennas which are only about one-forth of the length of those of C. morsitans, it is evident that these organs must play a very conspicuous role in the economy of the larva. As far as I can see, they are commonly but slightly developed in those species which live in extremely small water volumina (tree-holes, water reservoirs of plants etc.); they are also small in those species which mainly find their food at the bottom of the ponds or upon plants; with regard to the large, beautiful, many-rayed tufts, which occur in those species that find their food in the water layers, where they produce a circulation in the water by means of the fan-shaped lateral hairtufts of the labrum, I have got the impression, that these large wheels bound a little water area, in which the water currents produced by the labrum come in ; the large wheels act as filters, preventing too large particles from entering the area immediately before the mouth parts. I assume this, because I have seen the wheels, when too large a particle has struck against them, turn suddenly round and jerk away the particles. It may be added that the antennae, especially in the lower part, are spinose; antennae without any spinosity we only find in F. geniculata. The Thorax, consisting of three fused body segments, is always broad and flat; the integument is membraneous, often furnished with two deep, longitudinal furrows. Along the anterior and lateral margin long hairs, single or in tufts, are in- serted. The arrangement of the hairs, single or in tufts, of the anterior margin, is of value as a means of classification. In the description of the larva.' I have used this character and by means of figures given the hairs their number and position. The hair formula of C. morsitans 231124421132 is to be understood in the following way: In the median line two hairtufts, consisting of four hairs; laterally two double; they are followed by two single hairs; then follows a tuft with three hairs, and at the extreme end a tuft with two hairs; twelve hairs or hair-tufts on the frontal margin may probably be the original number, but now and then one or other of these tufts are suppressed. The number is almost always largest in the median tuft, commonly three or four; then follows almost always a series of three or four single or double hairs, 12 and lastly at the anterior corner of the thorax a tuft of from two to five hairs; these frontal hairs are all long, stiff hairs, directed laterally and protruding beyond the brushes; in some species of the genus Ochlerotatus the median tuft consists of one long hair and two or three very short ones; the second tuft often consists either of one or two very short hairs, which may easily be overlooked. The lateral hairs are arranged in two large tufts, occupying the middle and hindangles. As Howard, Dyar and Knab indicate, they are situated on low tubercles and prevented from bending backward by a smal chitinuous plate. Near both tufts very long stiff single hairs are often inserted. On the dorsal side of the thorax we often find a number of small tufts of hair, commonly serially arranged; most probably they very often fall off after the moult; generally they have not been indicated in the figures. The Abdomen is long, slender and cylindrical; it consists of nine segments. The integument is membraneous, except that of the ninth segment; still it is much thicker on the dorsal than on the ventral side; between the segments the integu- ment is very thin and delicate; the first segments are always shorter and broader than the following ones, the seventh is commonly the longest; on the lateral bor- ders we find tubercles which support the lateral hairs. As it is well known, the motion of the abdomen is extremely high; the motion of the body is always side- wise, never dorso-ventral; when the animal is to rise from the bottom, the position of the body is vertical and the body is wriggled sidewise upwards; respiratory movements of the abdomen, as it is well known in the larvae of Chirononiidcv, Phryganida-, a. o. have never been observed. The six first segments bear long seta? on lateral tubercles; the number is greatest on the two first, on the others com- monly only one or two; on the dorsal side we find the so-called subdorsal hairs, shorter hairs arranged in two series, and most strongly developed from the third to the sixth segment. They are often wanting; mostly their number is two; in our Danish species they are generally rather inconspicuous and are well developed only in one single species, the one of the tree-holes F. geniculate); further, fairly well in the Danish species of genus Culex especially C. nigritulus. In F. geniculate! every segment, from the first to the seventh, bears three pairs of setae, an anterior, a median and a posterior one; the median pair is best developed and consists of four hairs in stellate arrangement. Owing to these groups of hairs the whole larva has a very hairy appearance. According to drawings and descriptions of tropical larvae it seems that luxuri- ous development of subdorsal hairs and hairs upon the thorax, mostly in stellate arrangement, is a very common trait in larvae living in tree-holes and in water reservoirs in Bromeliaceae and other plants. — At the base of the lateral hairs, groups of shorter hairs are often to be found. The development of hairs upon seg- ment seven is not so luxurious as on the preceding segments. The eighth segment is short and bears dorsally the sipho or respiratory tube; it bears three hair-tufts, one dorsally, one ventrally and one posteriorly in the cleft between the sipho and the anal segment; long stiff single hairs in varying 13 numbers are implanted between these tufts; the posterior tuft is best developed and always feathered, but all in all the place and the development of these hair-tufts are so constant that they cannot be used as characters for classification. A peculiar structure is the lateral groups of spines or scales; these scales are either arranged in a single line, as is the case with Finlaga geniculates and Tceniorhynchus, often, but not always, with .4. cinereus, or in irregular arched series, covering a triangular spot on the sides of the eighth segment; the largest number of scales is always in the anterior rows. The number of scales is very different in the species, but fairly constant in the same. It is only about from ten to twehve in F. geniculate/, Tamiorhgnchus Richardi; com- monly from twenty to forty in most of the Danish species of the genus Ochlerotatus, but about one hundred in C. morsitans; it seems as if the number is greatest in those species which have the longest sipbones and the best development of the flabella?. The base of the scales is always spatulated; they are often provided with one strong spine, two shorter laterally, and many shorter ones bordering the sides of the spatulated part; they may also as in some of the species of Ochlerotatus be broad plates, ending in from five to seven thorn-like prolongations of equal length. They are often laterally covered with a delicate, hyaline membrane, radiated along the borders. Their number, position and form are of great value as characters for classification; in the systematical descriptions they are determined as the comb. The significance of the comb for the animal is in my opinion quite enigmatical. The median spines of the scales may be rather long and very acute; still it is rather difficult to understand, how they can be a weapon for the larvae; where there are many scales, the comb impresses me as a carding apparatus, but I am unable to see, how the animal should use such an organ. Dorsally the eighth segment carries one of the most interesting organs of the Culicin larva?, the sipho; this is always strongly chitinized, of a dark brown or yellow colour; nearest to the base it has almost always a strong chitinized black ring. If we compare Tab. XIX of C. morsitans with Tab. II of C. caspius we shall see the great difference with regard to the dimensions even in a fauna so small as the Danish one. It is commonly about three times longer than broad but may, as is the case of C. morsitans, C. pipiens and C. nigritulus, be from five to seven times longer than broad; it is extremely short, almost intlated, in 0. caspius. At the apex we find an opening through which the larva takes air into its trachea?. The sipho is closed by a set of five flaps; when the larva comes up to the surface, the flaps pierce the surface of the water; then they are folded out and pressed against it; by means of the surface film the larva? hang down from the surface and draw the air into the trachea". When I have had different species isolated in vessels and have exam- ined the surface, from which the larva? were hanging, with the binoculary aquarium microscope I got the impression that the stars which the five flaps formed upon the surface had quite a different aspect in the different species. The form of the (laps and their bristles differ from species to species; but this can only be thoroughly studied when the larvae are killed with the Haps open, the sipho cut 14 off and arranged vertically on the slide, so that it is possible to look directly down- wards at the apex of the sipho. This is a very difficult process. The sipho carries hairs and thorns in different arrangement. On the basal third of the sipho are inserted two ventro-lateral series of spines, commonly determined as pecten. This organ is of great value for classification. It commonly consists of from twenty to thirty strongly chitinized spines, arranged on a line and at almost the same distance from each other; at the base they are dentated, carrying from one to six teeth; they may be flattened as is the case with F. geniculata, C. morsitans, C. pipiens and nigritulns, formed here as oblique feathered scales of brighter, almost yellowish chitin. In Theobaldia annulata we find no thorns, but only a series of long soft hairs, without any teeth at the base. In some species the last thorns, those nearest to the apex of the sipho, are at a larger distance from each other than the following; they are not dentated and often inserted out of line (Aedes cinereus, 0. diantceus, 0. lutescens, excrucians, diversus, prodotes). The position of these spines varies from species to species. In Tceniorhyncus the pecten is wanting (see remarks later on). Also the function of this organ is quite enigmatical. It differs from species to species; that it should have no significance whatever I regard as highly improbable. It has so great a similarity to a comb that it must be regarded as fairly probable that it may be used as an organ, by means of which the different hair-tufts may be cleaned. The hair-tufts of the sipho present some of the best structures for purposes of classification we have hitherto been able to find in the Culicin larva?. According to the drawings published by Howard, Dyar and Knab the tufts may be arranged very differently from what I have seen in the relatively poor Danish fauna; for a more thorough study I refer the reader to the above-named tables. In the Danish larva? the most constant tuft is the apical one, very near the apical end of the pecten. It consists of from five to seven feathered bristles. It may, as in 0. annulipes, lutescens and excrusians, be highly developed or, as in Aedes, be rather inconspicuous ; it may be wholly absent, but we then find another, equally well developed, brush at the basal end of the pecten (Theobaldia annulata, C. morsitans). In Culex pipiens and C. nigri- tulns we find four or five tufts with two hairs generally arranged serially and ventrally, but with one or two of the tufts out of line. Only in 0. rusticus four tufts of double hairs are inserted on the dorsal side of the air tube, opposite to the pecten. Dorsally near the apex is further inserted a short thorn; two of the flaps carry two short curved spines which are often used when the larva? rest on the bottom with the dorsal face downwards, or when they are hanging from or supported by waterplants. With regard to the modifications of the eighth segment of Tceniorhynchus I refer to my paper (W.-L. 1918 p. 277). The ninth segment or Anal Segment is out of plane and inserted upon the eighth segment. It is short, often almost isodiametrical, in F. geniculata shorter than broad, in Tceniorhynchus twice as long as broad. It is covered with a chiti- nous plate, short in the larva of the first stage, but in the fullgrown larva often rounding the whole segment, but mostly only covering about two-thirds of it. At 15 the apex it bears the anus, surrounded by four anal or tracheal gills, four appen- dages varying in size individually. In ponds situated only a few meters from each other I have found in one of the ponds larvae of O. communis with the gills only half as long as the anal segment; in another larvae with gills more than three times as long; they seem to be most strongly developed in water which is extremely dark and peaty. In some species, f. i. F. geniculate: and C. pipiens, two of them are much smaller than the two others. In F. geniculata they are remarkably broad, in 0. caspius and 0. detritus extremely short. Some authors regard these organs as having no respira- tory value, as being only of locomotorical significance, but most suppose that their main function is really respiratory. (Babak 1912 p.