" Se te pigetetnteodetedetetetietees..4 mb, pet bRekeGseetegenndarenela ne een ope Le pwn ~ ee Mistetareabsoseeter rane sehatentenene dis) ' f Seer ¥ rss mpeg hens IY pec casblteor ara Nene + HARVARD UNIVERSITY. LIBRARY OF THE MUSEUM OF COMPARATIVE ZOOLOGY H1H 50 eee te NV] - WW). LO oe Es Oforker a4, 1914 Wy a Ae i, Re \yals meow 2 Cn \ =» OBSERVATIONS ON PLANARI-, A GENUS OF AQUATIC ANIMALS. : ba, ay nt e HAS i ‘ 4 Ax, AP RNUQA, 10 BUMG AS ie Kan Or > Wlizars Delt P. Syme.t OBSERVATIONS ON SOME INTERESTING PHENOMENA IN ANIMAL PHYSIOLOGY, EXHIBITED BY SEVERAL SPECIES i PLANARI. ILLUSTRATED BY COLOURED FIGURES OF LIVING ANIMALS. BY JOHN GRAHAM DALYELL, Esa. EDINBURGH: PRINTED BY ANDREW BALFOUR, FOR ARCHIBALD CONSTABLE & CO. EDINBURGH ; AND LONGMAN, HURST, REES, ORME AND BROWN, LONDON. 1814. nt gan uve edo | hey i ih a: at TARO! Bi eae G 2 Vb BOS 0 ih uk Adm ARE ATTA MCZ LIBRARY _ _ HARVARD UNIVERSIT PREFACE. Tur following Observations are chiefly extracted from a journal of incidents in na- tural history, kept as occasion offered, du- ring several successive years. Many in- terruptions opposed their progress; the concurrence of circumstances indispensible for connected detail were frequently want- ing; experiments were rendered abortive by casualties ; and hence the imperfections which they now exhibit. Nothing is referred to but what has ac- tually been witnessed, which is a better means of promoting the progress of science than resorting to the auxiliary authority of other naturalists. Dates are given to aid the illustrations, not to claim any priority of observation, were such even worthy of A Vi PREFACE. appropriation. Possibly, analogous enqui- ries have long ago been instituted by those more qualified for the task ; and, what has appeared obscure in the nature of the ani- mals now brought under consideration, may already be elsewhere satisfactorily explain- ed. The Figures, which will elucidate the subject where verbal description fails, have invariably been drawn from living Planarize in motion, and generally after having fed, as the most ample view of their organiza- tion is then presented. Naturalists, who take these animals indiscriminately from their native abodes, may therefore find dis- crepancies, resulting from a state of absti- nence; and variations still more conspicu- ous may appear, from the unequal evolu- tion of nascent parts. But experience will speedily inculcate, where, after passing all the successive stages, perfection at length is gained. Nevertheless, the size is some- what less than life, because Planarize always decline in a state of confinement. The name of any species distinctly re- cognized is retained; and if a new one is bestowed on those where this is doubtful, PREFACE. Vil it is only to put their identity beyond fu- ture dispute. It cannot but appear remark- able, that peculiar difficulty should have been experienced here; that a certain genus should be instituted, and a number of species, all distinguished by individual characteristics, brought under it, which ‘scarcely, in a single instance, demonstrate the place to which they belong. Yet this will appear less surprising, when we reflect that the site of an organ, the most import- ant assuredly, the mouth, has hitherto been referred to the anterior extremity in all, instead of the middle of the belly, its general position. Although the Observations which occupy these pages lead to very different conclu- sions from what such eminent naturalists as Linnzeus, Cuvier, and perhaps the learn- ed and indefatigable Muller, have endea- voured to deduce for the purpose of sys- tematic arrangement, names so celebrated ought. not to be mentioned without the utmost deference. Had the genus Plana- ria engaged their protracted investigation, the phenomena now exposed would not have remained so long in concealment. Vill PREFACE. The errors which have darkened the beautiful science of Natural History, are principally to be traced to superficial ob- servation: and if this be true with regard to the larger animals, how is it to be ex- pected that the smaller have received that scrupulous care and attention, by which alone their habits can be illustrated? Scarce deemed worthy to hold a place in exist- ence, they have been obscured by more conspicuous objects, those whose properties it required less time and labour to unfold. But the real Physiologist, who knows the universal balance preserving the scale of animation, and who feels the imbecility of his own understanding, in scrutinizing the operations of Nature, will not presump- tuously depreciate what are called her meanest works. Each has its appointed place, and its appointed purpose. Patient enquiry is the only unerring guide; and even this may be defeated, unless a com- bination of incidents shall favour the ob- server. Perhaps it is less from the number of animals, than the accurate examination of those brought under review, that benefit PREFACE. ix accrues to science: nor can simple refer- ence to a particular class, from external conformation, be accounted of equal import- ance to watching the properties disclosed by living nature. Hence the great neces- sity that animals shall be preserved in that condition where all the vital functions, un- restrained, can be fully displayed ; where we shall be enabled to behold the united operation of instinct and organization. Though reasoning on facts which can ad- mit of no mistake be thus reduced to the result of time and industry, our cares are rewarded by banishing precipitation, which is ever prejudicial to philosophical enquiry, and hostile to the discovery of truth. ti aa et ei ae pnw havandgia eh oh | ~ vail pane ad gallon ‘ } ag ‘edagh: Us rt Eee iri i ae eh Kish re aii 1m | A i basiett oe nur y bid Hal a et a OM “Uf aa up te th, omen ie “ie OS hed d i both pay ‘ie. f al Ua } 4) ™ ey ehs aga page anid fi a ain ilo ita so t 5 il Sane. ad as bea a Lvigtoak th vag Z Meee aieh sha ia A Me ye We, Wal Ras sae ue ah’ es a BS Tae. Bee CONTENTS. Page. Pemaria Mlewilis. ec oh ees wees) Maan a TEA INTO. oo eae a ake 23 Pinvaria Panniculata, 0.0. i ee 37 eer TOM CLINE. 8 eta!) oaks oA Mis ane 42 eimnaria Arethisds, ees Oe Se OE 85 PRUOIIG: GrOHViNeds ooo css bis ae ls 114 PV EROTIO. VELOUR 1 i lal oo oak oe ee ee go voy PUGRAP A TLAMERSIS oS Ore A. 133 Eaplanation of the Figures, 2... 6. e 145 Sit Aci che aim if v My OEE Maura A wat { wee LAAN Mir he ya Dates with’ | (oor aed “SAD Ye. tr ae AOE uF Saher Aue we -oacined ke sa Wo nga OBSERVATIONS ON PLANARI &. Ow descending from terrestrial objects to the inhabitants of the waters, infinitely new and interesting matter is presented for the contemplative physiologist. Myriads of beings, alike singular in structure and pro- perties, appear in their peculiar element, all actuated by the resistless impulse of na- ture ; avoiding danger, seeking subsistence, rendering the weaker a prey. But figure, habits, and instinct, are not their sole cha- racteristics ; they enjoy privileges besides, which we might be prone to account so ma- ny aberrations from the laws of organiza- B Z NATURE OF PLANARIZ tion ; while the test of experiment unfolds latent phenomena, which the utmost efforts of human ingenuity find it difficult to illus- trate. Certain animals, though liable to perish by simple evaporation of their sur- rounding fluid, can, in other circumstances, endure privations apparently inconsistent with life itself. What prove deadly wounds to the majority of the creation, only serve to awaken in them the active principle of an inexhaustible reproductive power. The perpetuation of their race is effected by means the most remote from those that usually regulate the origin of animated ex- istence. A shapeless fragment is disjoin- ed from the body of the parent ; it remains in quiescence more resembling the state of death : but new organs are gradually evol- ved—motion is resumed—and all the qua- lities successively displayed which belong- ed to the primitive whole. z Such are some of the admirable preroga- tives conferred on the creatures about to be described. Let us not anticipate them NATURE OF PLANARI£. & farther, lest, in obscuring the fragility of their texture, we may be erroneously led to deem them, of all others, the chosen works of the universe. Animals with soft bodies, wanting bones, are divided into several subordinate tribes, one of which, either from external configu- ration, or a smooth gliding motion over even surfaces, has been denominated Planaria. All the species with which we shall be oc- cupied are strictly aquatic ; the presence of water is equally indispensible to their safety and preservation ; for contact of the atmospheric element, though during the shortest period, is irremediable destruction. Some dwell in the sea; others inhabit lakes, marshes, and such streams as are almost still or undisturbed: and it is also said that they may be found in humid meadows ; but none of that description have come within the sphere of my research. Perhaps the genus is as yet insufficient- ly characterized; nor will the subsequent remarks do more than approximate it to its 4 NATURE OF PLANARIZA. proper place, in the order of nature. Cer- tain species now excluded, ought obvious- ly to be annexed to it; and _ possibly seve- ral which are there comprehended, should be detached. Adjusting this point, how- ever, would involve discussions which it may be desirable for the present to avoid. The planaria, on external inspection, seems allied both to the leech and the snail, but more akin to the latter, and, at the same time, possessing parts and properties belonging to neither. Intermediate ge- nera probably remove it from each; for, as our knowledge of the creation ex- tends, subordinate distinctions produce an interval between analogous races of ani mals, occupied by shades always becom- ing slighter and slighter, until the origi- nal characters are lost in some common object. One comprehensive division, that which shall engage most of our attention ~ in this place, may be defined, “ naked, flattish in a state of abstinence, provided with a proboscis protruding from the mid- PLANARIA FLEXILIS. 5 dle of the belly or under surface; swim- ming supine.” Another division may be defined, “ body in a state of repletion, re- sembling a double cone ; mouth in the an- - terior extremity.” Division I. Planaria Flevilis, Fig. 1, 2. Near to low-water mark on the shores of the Forth, we find a species of these ani- mals, universally of a dull whitish or pale ash colour, about an inch long, and a quar- ter of an inch across at the extreme breadth. The whole body is quite flat, especially be- low, almost as thin as paper, and endowed with singular flexibility. The head is se- micircularly obtuse; and, from near its ante- rior extremity, the body decreases to the termination of the posterior part or tail, which is also obtuse, but proportionally much less so than the head, and is sometimes dimi- nished to a point. The contour of young planarize tends to the outline of a spheri- cal triangle, which gradually alters with their increment. By an uncommon distri- bution of the most important organs, the 6 PLANARIA FLEXILIS. aperture of the mouth, unlike that of ter- restrial animals, is remote frem the head of the planaria. Situated in the belly or un- der surface, nearer to the tail than to the anterior extremity, it receives the necessary aliment to be transmitted to the viscera. Some remarks will afterwards occur on the singular proboscis with which this division of the genus is provided, when treating of those species where its structure has been more easily examined. Towards the an- terior part are two blackish spots on the upper surface of the body, which being subjected to the microscope, are discover- ed to be two groups or clusters of minute jet black specks, of unequal size, and like- wise of unequal number in different ani- mals. In one planaria, each cluster con- sisted of eight specks; in another, of four- teen or sixteen; and in a third, which was very small, of eighteen or nineteen, seve- ral being deeper seated in the body than the rest. These specks approach to a glo- bular figure; some are apparently confound- ed together; and they occasionally appear PLANARIA FLEXILIS. 7 singly, advanced in a straight line from the respective clusters. Microscopical ob- servations are attended with extreme dif- ficulty, owing to the incessant motion of the creatures, and the necessity for their being kept in water; and they contract so much when exposed to cold, that render- ing them torpid is of little utility. It may here be remarked, that the exa- mination of pale and pellucid animals with lenses, is greatly facilitated by their inter- position between a dark groundand the mag- nifier, as also that it should uniformly take place by day. All the artificial light which the combination of combustible substances can produce, is infinitely inferior to the slightest gleam of sunshine, or even what is transmitted from a clouded sky. The higher the magnifying power, the greater the consequent obscuration of the object, which proves how dependent our know- ledge of its structure is on the degree of illumination that it receives. Whether these specks be truly eyes, or 8 PLANARIA FLEXILIS. what is their peculiar use, is uncertain ; nor can we determine whether the impressions received, or the functions performed, rest on their united operation. Their remote- ness from the mouth may be thought un- favourable for aiding the animal to the cap- ture of its prey; and their position so far from the portion first advanced, seems ill calculated for enabling it to avoid danger. Naturalists are prone to ascribe the same faculties to those organs of the smaller tribes, which bear a distant resemblance to the place and appearance of eyes in the larger animals. But the precise nature of vision in all aquatic and terrestrial insects, and likewise in the whole mollusca and vermicular race, is exceedingly obscure ; and, notwithstanding our readiness to be- stow it on many of them in perfection, there is certainly ground to dispute, whether we are acquainted with any particular organ appropriated for it. Perhaps this sense is not indispensible to their security or pre- servation; many animals seldom approach PLANARIA FLEXILIS. 9 the sphere of the solar rays; all the won- derful operations of the bee are conducted in the dark. Most planariz court the light indeed ; but the flexilis rather inclines to shun it, less, we may conjecture, from being warned of its presence by the specks er eyes, than from some disagreeable sen- sation produced on the body. Apparently, the vicinity of food is recognized more from an analogous impression, whatever sense may be affected, than from vision. The body is surrounded by a smooth narrow margin, paler in colour than the rest, and of a different texture, participating, ina minor degree, of the gelatinous consistence which composes the general substance of the whole genus. From these character- istics, the species can hardly be mistaken, particularly as there is no other animal known to us that resembles it. The size of each individual is materially affected by the external temperature, and the food absorbed. As the day is warmer, the planaria is larger, and it sensibly di- 10 PLANARIA FLEXILIS. minishes with the approach of cold. Thus, the specimens delineated in the annexed Engravings are not of the extreme dimen- sions, which may unquestionably be aug- mented by a copious and regular supply of aliment, independent of the temporary in- crement attained. Temperature and food must always be taken into account, in speaking of size, for both contribute to en- large the contour of the body. Besides, it essentially merits consideration, that the colour of the entire animal is principally regulated by the tinge of the aliment re- ceived ; and if we say it is naturally of a dull white, this means in a state of absti- nence. Its proper abode, however, being among mud, that substance promotes a tawny hue; for, on removal from it, pla- narize become much clearer, and, in com- mon with some other animals under simi- lar circumstances, almost white. As the tide recedes, they recede along with it; and if accidentally left behind, take shel- ter beneath stones on the shore. PLANARIA FLEXILIS. | 11 Planarize, like most marine animals, de- sert their haunts at night, and range ac- tively around in quest of prey. An incre- dible change is produced in their appear- ance by the immoderate quantities they devour, insomuch that they can scarce be recognized for the same beings. I was particularly unsuccessful in endea- vouring to discover the proper food of the planaria flexilis ; every different substance was rejected ; and, in the interval thus oc- cupied, all the animals successively procu- red gradually wasted away to extenuation. It occasioned me the greater regret, from their rarity in the districts within my reach; and experience had taught me, that the most essential condition which can aid in- vestigations into the phenomena of ani- mated nature, is ascertaining the aliment whereby life is preserved. A new oppor- tunity having occurred on the 31. of Au- gust 1809, three planarize, after an absti- nence of several days, were supplied with the heart and liver of a perch; the sea wa- 1 12 PLANARIA FLEXILIS. ter was changed, and a quantity of mud put into a glass jar along with them. Next morning a material alteration had ensued: the colour of the largest was altogether al- tered from its original dull and tawny white, to dark reddish brown. Numerous ramifications, beautifully interlaced, were distributed throughout the body, proceed- ing from the centre to the interior of the narrow margin, into which they did not pe- netrate, and the size of the body was aug- mented. This could be ascribed to the quality of the food alone ; and it also shewed, that the animal was carnivorous. Other experiments followed; and some time afterwards, the same planariz having devoured a green marine nereis, a creature of soft consistence as themselves, their bo- dies became of a greenish hue, which three or four days were required to obliterate. {t is alike with each variety of food: the colour is constantly imparted to the animal ; and nothing can be more elegant and inte- resting than its dissemination among the PLANARIA FLEXILIS. 13 numerous pinnate and delicate shaped ves- sels performing the functions of nutrition. But the naturalist cannot be sufficiently guarded against yielding to appearances : none are better calculated to mislead his judgment than those which are now exposed. I have oftenerthan once taken planariz of se- veral kinds,embellished by complicated rami- fications below, and above exhibiting a tinge different from what had been seen in any other species. Neither did their size corre- spond with the dimensions of those which might be deemed most analogous; and leven thought there was a sensible peculiarity in their motion. These facts would have war- ranted the addition of another species, or at least a variety to the genus; yet, having preserved the individuals a day or two, an al- teration both of figure and colour augment- ed the difficulty of condescending on their proper place, until the further lapse of time brought them to my knowledge as animals quite ordinary and familiar. Whence did the discrepancies arise ?. From the quality 14 PLANARIA FLEXILIS. of the food alone, and its subsequent assi- milation with the substance of the plana- riz. The peculiar colour impressed on the observer, was from at first sight con- founding the infinite ramifications with the general mass of the body: the size had been affected by a copious supply of ali- ment ; and as motion is accelerated or re- laxed by the pressure of necessity and ex- ternal temperature united, some unusual combination had operated here. Along with the disappearance of the food, the co- lour vanished ; the size was, from the same cause, reduced to its accustomed limits: hunger stimulated to action; and animals, identically such as I was wont to behold, were before me. This is a cogent illustra- tion of the advantage of leisurely awaiting the alteration which may be undergone by beings so susceptible of change. All the planarize that have come under my inspec- tion, would seem, to a superficial observer, quite different species in a state of absti- nence from what they are in a state of re- PLANANIA FLEXILIS. 15 pletion. Probably the acute and intelligent Muller, to whose researches naturalists are so eminently indebted, did not escape that liability to error which accidental appear- ances are calculated to produce ; for what are in some instances given by him as per- manent characteristics, would most likely have been obliterated with long intervals of observation. The alimentary matter absorbed, is im- mediately received into large viscera, and distributed entirely throughout the body, as is proved by the ramifications being co- loured : and in this the nature of planariz differs from that of the larger animals. It is not the sensible parts of the food taken into the stomach which are transmitted to the extremities of the latter ; but, by some mysterious process, their beneficial influ- ence is universally disseminated. In pla- nariz, on the contrary, instead of a nutri- tious principle only being diffused from the intestines, or the organs analogous to those connected with a stomach, portions, and these in considerable quantities, of what 16 PLANARIA FLEXILIS has actually been received, reach from the center to the margin. Planarie, “in the natural state, perhaps feed on the mucilaginous parts of vegeta- bles; they are likewise carnivorous in the highest degree, greedily devouring animal substances, particularly the softer kinds, as mussels, oysters, and others of the mollusca tribes. Unless a certain temperature pre- vail, all aliment is rejected ; and when the thermometer stood at 45°, with chill winds, it has been necessary to remove them to a warmer atmosphere, where they readily fed. Nevertheless, they sometimes refuse food for weeks together, though in a favourable situation. Their voracity is incredible: the whole flexile body is employed in firm- ly infolding the prey: if living, its strug- gles are vain to get free; it Is gradually absorbed, until the capacity of the viscera can receive no more. But, contrary to what is witnessed in other animals, of which the belly protrudes with repletion, the back of the planaria rises in proportion to the PLANARIA FLEXILIS. 17 contents of the stomach, and frequently it carries a hump a quarter of an inch high. One of three planariz which had been co- piously supplied with food, proved incapa- ble of swallowing the whole quantity that it had attempted, whence some part re- mained protruding from the body. In this condition, the animal, as well as the others, which had manifested nearly equal voracity, sought the surface of the water, where they lay supine and motionless. About thirty hours afterwards, two of them exhi- bited a singular spectacle: a wide rent ap- peared in the middle of the body, tearing it almost asunder ; while each endeavoured to liberate itself of the half-digested food ; and incipient rending nearer the edges was also perceptible in the upper part of the third. Previous to so unexpected a conse- quence of repletion, indications which I have never been able to verify, induced me to suspect the probable existence of apertures in different parts of the animal, whereby the food proving incommodious or c 18 PFLANARIA FLEXILIS. indigestible, might escape before its natu- ral dispersion among the vessels. The three planarie at length literally seemed burst from their excessive voracity ; and a portion of the tail of one was tore away in its struggles. Notwithstanding every pre- caution for their preservation, all perished within two or three days ; and putrefaction rapidly dissolved their lacerated bodies. Some animals, especially those whose success is uncertain In capturing prey, can survive wonderfully long entirely devoid of aliment. But when the opportunity comes, their voracity is proportioned to the absti- nence endured. Adhering to the same spot, the polypus and sea anemone can on- ly extend their retractile tentacula to seize whatever victim may occasionally stray within their compass. A wide mouth expands beyond the diameter of the base to receive it; the capacity of the body is dilated infinitely above its ordinary di- mensions; which are again reduced as the food is consumed by digestion. No ani- PLANARIA FLEXILIS. 19 ‘mal, however, in so far as I have witness- ed, except the planaria, actually sacrifices its life to its inordinate appetite. These planarize dwell in society: they are of an extremely pacific nature among themselves, and very inactive, unless when in pursuit of prey. Then they may be seen traversing their element with a remarkable motion, produced by the successive open- ing and closing of the broad anterior part of the body. They generally live half buried in mud, a substance with which the vermes and molluscze should constantly be provided, particularly those undefended by any ex- ternal covering ; but it should be pure and unmixed with fragments of vegetable mat- ter. The smoothness of its surface pecu- liarly corresponds with the soft and deli- cate texture of such creatures; and they should also be kept in glass vessels, as earthen-ware, though fine in quality, is of- ten too rough and unequal for them to pass over, without suffering. A frequent change of sea-water is beneficial, and it should al- 20 PLANARIA FLEXILIS. ways be renewed soon after the planariz have fed, for an insensible putrescent prin- ciple is imparted to it by their most salu- tary aliment. On the water becoming fe- tid, they rise to the surface, and endeavour to escape; thus pointing out an easy me- thod of dislodging marine animals from their recesses. By rendering sea-water noxious, from the gradual decay of putrefying sub- stances, they desert their haunts, other- wise’ inaccessible, in quest of some more ge- nial element ; or, if a tall glass jar be filled with a promiscuous mixture of mud and vegetables from a fresh water marsh, many of its inhabitants will be seen ascending the sides towards night, though, on the ap- proach of day, they return to places of con- cealment. The natural mode of propagation by the Planaria Flexilis, seems from eggs: whe- ther each animal is a hermaphrodite, I have not been able to ascertain ; nor, indeed, all the peculiarities attendant on the perpetua- tion of their race. Some, which had been PLANARIA FLEXILIS. 21 kept several months, appeared in unusual agitation on the twenty-fourth of Decem- ber ; and then a small spot of very minute eggs, as I conceived them, was seen on the side of their glass, near the surface of the water. Between that day and the tenth of May, the Planarize continued laying, un- til the eggs amounted to thousands pro- duced by each. They were preserved with much care, but I could not be sensible that any young were hatched; and at length I conjectured that many of the eggs were de- voured by the old ones. Circumstances have prevented a repetition of this obser- vation, which demands to be further illus- trated, as the nature of the Planariz was affected by the heat of an apartment, and they were not isolated. For a long time, the original spot was resorted to ; the eggs, if they may truly be considered such, were afterwards affixed to various other _parts of the vessel. Whether more would have been produced after the tenth of May, is uncertain, as all the Planarize perished about that period. A premature season 29 PLANARIA FLEXILIS. was probably hastened by their artificial si- tuation. The Planaria Flexilis is one of those be- ings so eminently privileged, as to preserve animation when divided into sections: If cut asunder, each half acquires the de- fective organs. At first the posterior portion is quiescent ; and a considerable in- terval elapses before its motion and activity are resumed: the anterior division suffers little ; it traverses its element as if scarce affected by the mutilation ; a thin triangu- lar vegetation proceeds from the wound, which is gradually enlarged, and at last ac- quires the exact figure and proportions of the severed parts. The longest period during which I have at once preserved these marine Planarie, has exceeded eight months. As accident then deprived me of them, we are not to conclude on the brevity of their existence. Indeed, the life of most aquatic animals is by no means short; and perhaps the ter- restrial molluscee, and some apterous in. PLANARIA NIGRA. 23 sects, infinitely survive the term which we generally conceive appropriated to them. It is accident that abridges life; seldom the simple decay of nature. Planaria Nigra, Fig. 8.5.15. During the sunshine of summer, a small jet black velvet-skinned animal may be often seen crawling near the edge of fresh-water ponds and ditches, with a lively, smooth, and glid- ing motion. This is the Black Planaria, which has already been characterized and described by different naturalists ; but, un- fortunately for that accuracy which should mark the progress of science, their superfi- cial observations concerning it have led to those numerous errors which darken the history of the whole genus. Sometimes it is found in slow running waters, and there of the largest size, but usually when they are almost stagnant, and, in particular, where aquatic plants abound. On these, numbers crowd toge- ther as the colder season advances, each a4 PLANARIA NIGRA. contracting into an elliptical spot, and then affording the most favourable opportunity for many being taken with facility at a time; or they fix on the under surface of pieces of slate and smooth stones somewhat ele- vated above the mud. They live in nu- merous pacific societies, associating with every other species: and are so generally dispersed, that none has occurred to me of such frequency in Scotland. An animal so well known as the Black Planaria scarce requires description; nor, considering its external uniformity of ap- pearance, does there seem much room for commentary. It is found of all different sizes, from extreme minuteness to above half an inch in length, and about an eighth of an inch in breadth. When very large, it has a dull and sluggish aspect, and is chiefly roused to action by light and heat. On the under part, or belly, are what natu- ralists have designated two ventral pores, one of which,---perhaps both,—is more con- spicuous at certain seasons. The first is PLANARIA NIGRA. 95 iower down than the middle of the body, and the second still nearer the extremity of the tail. The opacity of the animal precludes us from accurately distinguish- ing its internal organization ; nevertheless, enough may be discovered to infer, that it is far from simple. Among black Planariz, some occasionally occur of the ordinary size, figure, and proportions, but, instead of the jetty colour proper to the species, they are of a dark grey. By interposing them between the eye and concentrated rays of light, the internal structure may be ob- scurely recognized in many vessels, branch- ing from about the middle of the body, and terminating in obtuse extremities near the margin. These are certainly analogous to the pinnate ramifications already descri- bed; and they bear much resemblance to the viscera of leeches. Facts do not war- rant our concluding that the grey Planarize are indubitably a different species, or that they are only varieties ; their contour seems more ovate, indeed, and they are seldom if 26 PLANARIA NIGRA. ever seen of the largest size. One taken in October was of light grey and mottled, or streaked with deeper transverse bands : it was very broad in proportion to its length. Yet it must be admitted, that repletion al- ways affects the colour of the leading spe- cies, which regularly darkens according to age and increment. Probably, from disten- sion of the vessels, shades of difference may prevail, which temporary causes render more prominent. | The Black Planaria is endowed with wonderful tenacity of life, a property which materially aids the researches of the phy- siologist. The truth is forcibly demonstra- ted, by the dreadful lacerations with which it appears in its natural element. Some- times a large section from the neck is wanting, sometimes a semicircular wound almost divides the animal asunder, or one half of the body has been tore from the other, and still it survives the mutilation.— This was a sufficient guide. The genus had been partitioned by nomenclators, according PLANARIA NIGRA. 27 to the number of eyes, or their total ab- sence; and a place from the latter was as- signed to the black planaria. It was pro- bable, however, if eyes were present, they should not be sought in the full grown ani- mal, which might be of equal opacity to themselves ; or, in other words, they would more easily be detected in regenerating parts : and, if such lacerations as I had wit- nessed did not destroy the animals, nei- ' ther would artificial separation of important organs be fatal. Several planarize were therefore decapitated on the tenth of Sep- tember ; and, in nearly three weeks, the wounds of some being examined by a mag- nifier, appeared not only completely heal, but a conical reproduction of the defective parts protruded. The regenerated organs of all animals are light and colourless ; and I thought that a row of minute marginal specks, such. as are usually called eyes in the vermes and mollusce, was discernible. This proved no illusion, for, on the twenty- ninth of the month, they were distinctly 28 PLANARIA NIGRA. visible, of a jet black colour, seated in a pale ground. Other experiments corrobo- rated the fact; whence, one characteristic of the species under discussion, is a row of nu- merous minute black specks or eyes, situ- ate in the very margin of the anterior part. The same reserve in ascribing the faculty of vision to these specks, is as necessary In this instance as before ; nor can we affirm, on denying them that peculiar province, that they are void of all analogy to spira- cula, or organs connected with respiration. A subsequent examination of those plana- rize just mentioned as a possible variety, shewed that the head is sometimes so light, as faintly to expose the site of the specks. Thus, if the genus is to be partitioned ac- cording to the presence or absence of eyes, the black planaria will be removed from the place hitherto assigned to it. In the course of my earlier observations on this animal, many unsuccessful experi- ments were made to discover its food, which seems chiefly derived from the under sur- PLANARIA NIGRA, 29 face of aquatic plants in vigorous vegeta- tion; and animal substances are likewise voraciously consumed. The sexual union takes place with the black planaria, though rarely to be witness- ed; nor had I complete conviction of the fact before August 1812, notwithstanding preceding incidents had led to such an in- ference. Long anterior to that period, I knew that this species propagated by eggs, which, for the most part, are laid by those of larger size, and usually in the course of autumn; but they may occasionally be found throughout the year, or obtained in winter by the more genial temperature of an apartment. No external characteristic distinguishes the male and female planaria, if there be actually a difference of sex be- tween them: that which is represented here, produced an egg, which entitles it at least to the character of female ; and what I supposed the male, was probably not quite so large. The egg is imbued by a yellow- ish viscous matter, attaching it to any twig 30 PLANARIA NIGRA. or straw selected for the deposit, or thé side of the including vessel. It is of a per- fect oval figure, of a dark brown or choco- late colour, provided with a hard shell, and in every respect exactly resembles a bird’s egg in miniature. Those of the largest size, for great inequalities prevail, are about a tenth of an inch long; and one of this description is seen, somewhat magnifted, Fig. 4. I cannot confidently affirm that more than a single egg is produced by each planaria; but each egg contains several young, of the palest grey, or almost white: their anatomical structure is then best dis- closed, as they speedily darken by succeed- ing increment. Some, hatched in the se- cond week of September, were deep grey on the fourth of October. The specks or eyes may be recognized at an early stage, by a magnifier, Fig. 5. which also exposes slight discrepancies in shape, between the young and the adult animal. A consider- able interval elapses before exclusion of the young planaria; but observations on the PLANARIA NIGRA. 31 period seldom coincide. By the most re- cent, four were detected in the very act of issuing from the egg, on the eleventh of April, twenty-five days after it was laid: all lively, the marginal specks very distinct, but not of equal number. An egg of the same species was at the same time hatch- ed in twenty-one days: but a fortnight later, a third of the like age was still entire. Therefore, the period required for exclu- sion, is to be calculated at twenty-one days, or longer; and it is certainly affected by the temperature of the atmosphere. The oviduct and relative organs appropriated for perpetuation of the species, are most like- ly situated in the second ventral pore: neither this nor the first is conspicuous in all planariz; in many they are scarcely perceptible, and appear connected in some by a lighter line on the abdomen. But, independent of propagating by eggs, the black planaria, from that indestructibi- lity of life preserving it under mutilation, is privileged to multiply its species in pro- 1 32 PLANARIA NIGRA. portion to the violence offered to its other- wise delicate frame. It may almost be called immortal under the edge of the knife. Innumerable sections of the body all be- come complete and perfect animals: if the head be cut off, a new head replaces it: if the tail be severed, a new tail is acqui- red: nay, if one half of the whole animal be longitudinally separated from the other, the defective portion is speedily repaired. A grand and leading law of nature is in- variably to fulfil her original object ; whence we must conclude, that the permanence of accidental lacerations, which we occasion- ally witness, results from some unknown condition opposing the progress of repro- duction. In the artificial mutilations, whose advances can be watched, the pe- riod of renewal is strictly commensurate with the temperature of the atmosphere. Regeneration is retarded, or altogether sus- pended, by the cold of winter; promoted by the heat of summer; and still further ac- celerated by augmenting the natural PLANARIA NIGRA. 33 warmth of the air. A number of planarize mutilated on the twentieth of January 1803, had become entire animals in the succeeding April: but all the new parts were of a lighter colour, which was long of approaching the sable hue of the old: and it may be question- ed whether they ever grow equally dark as those regularly deepened by age. Thus we see a black head, with a light coloured tail; a dark body, with a white head ; and one lon- gitudinal half black as jet, while its corre- sponding portion is of clear grey. The ele- mentary parts of all animals seem colourless: their future opacity is derived only from cer- tain assimilations of extraneous substances, the atmospheric influence, or supervening ri- gidity of the parts. Pellucidity marks the rudiments of life: fishes are transparent on exclusion from the egg; insects are pale on leaving the chrysalis; their organs are in- firm, and their senses obtuse. But scarce have they experienced the genial effects of the air, when their members expand, strength is acquired, and instinct becomes D 34 PLANARIA NIGRA, active; all as the universal shade of the body darkens. Yet exposure to the atmosphere, unmixed with another fluid, is inevitable destruction to the planaria. If, chancing to wander beyond the confines of its native element, its endeavours to return be inter- rupted, it contracts and grows distorted, a kind of gluten issues from the whole body, and death speedily ensues. Should it be hastily removed, it may recover, and then the gluten comes off like a sheath, or inte- gument, investing the body; but the tran- sition must be immediate. Whether this substance be provided by nature, to avert the baneful effects of unguarded exposure, or exudes in consequence of the sufferings of the animal, is uncertain. In the natural state, the planaria proba- bly survives the cold of congelation ; yet it perished during the course of an observation, where the thermometer stood at 26°, and where it was imbedded in a solid mass. of ice. Perhaps the change was too sud- den; for numerous societies dwell in shal- PLANARIA NIGRA. 35 low waters, affording an insecure retreat from the rigour of the atmosphere ; nor are they diminished in succeeding seasons. The bodies of those which perish thus, are distorted, stiff, and invested by-a very thick coating of gluten. Ina few hours after so- lution of the ice, they become soft and re- laxed, and are quickly decomposed. Monstrosities sometimes occur in the black planaria, and frequent distortions from casual injury. In 1808, one was found with the tail bifid ; a ventral pore appeared in each portion, both of which might be considered members of the same body. Accident may give birth to superfluous parts, as well as the skill of the experimen- talist; but this species, perhaps from the energy of its reproductive powers, seems less adapted for acquiring them. In addition to what has been said of va- rieties, we may observe, that a few are ta- ken in places inhabited by the black plana- ria, of smaller size, the head rather more obtuse, and the tail suddenly drawing to- 36 PLANARIA NIGRA. wards a point; whereas it ordinarily forms a regular elliptical outline, unless when pro- duced to an acute angle by extreme exten- sion. Possibly, however, the difference may centre in the progress of reproduction, whereof the commencement has not been seen. Very minute dark or light grey pla- nariz sometimes dwell along with the rest, of which the tail is more acute in propor- tion than that of the larger ones. Three of these, a line and a half long, being sub- jected to the microscope, traversed the. glass slider with great rapidity, much ex- ceeding the usual progression of the black planaria. A scanty row of very dark specks environed the anterior margin ; and the in- ternal organisation was sensibly exposed through the gelatinous texture of the body. But a series of experiments would be requi- red to entitle us to deny their identity with the young of the common species; first, be- cause the accelerated motion might be ex- cited, from the susceptibility of a small quan- tity of water, of an increased atmospherical PLANARIA NIGRA. 37 temperature; and secondly, from it not be- ing improbable, that the number of margi- nal specks is augmented with age: Superficial cbservation of such diversities only create embarrassment; for as the shades of distinction are fainter, there is the more difficulty in condescending on, or rejecting identity. The planaria, Proteus like, in- cessantly assumes a variety of forms and appearances, which, without due and care- ful appreciation, will lead the naturalist far- ther and farther from the truth. Planaria Panniculata, Fig. 6. 7. There is a species of planaria, narrowly resembling the former in size and figure, but different in colour, and frequenting different aquatic plants, on which it always appears as hav- ing enjoyed a copious supply of food. When recently taken, it is of a flattish semi-cylin- drical shape; the head forms an obtuse tri- angular outline, and is smaller than the bo- dy ; and the neck is smaller than the head. The whole animal is of a deep dusky brown, 38 PLANARIA PANNICULATA. so dark, as in some individuals to approach to black; and on accurate examination, it proves to arise from short black lines in a lighter ground. Many of these planariz are distinguished by one or more large irregu- lar patches of white, either above or below, and at times traversing the entire sub- stance to both surfaces. This, however, is not a universal characteristic, and when at either extremity, may readily be taken, by inexperienced observers, for regenerating parts. A broad dark line below, apparent- ly denoting the site of an intestine, pro- ceeds from the origin of the head to the se- cond ventral pore, which, as well as that above it, is extremely conspicuous; but, as has already been stated with respect to the preceding species, neither orifice is equally displayed at every season. The verge of the anterior extremity is environed by a row of most minute black specks, or eyes, scarce discernible by a magnifier of mode- rate power. One of the planariz having occurred with the patch so situated as to PLANARIA PANNICULATA. 39 engross a number within its limits, admit- ted of their inspection by the microscope ; and, when greatly enlarged, they exhibited an irregular figure, and uncommon inequa- lity of size. This planaria is not one hundredth part so common as the former, in places to which I have had access, perhaps from its favou- rite plants being rare; and I remember when pursuing such investigations, that, in a certain pool where the black planaria was numerous, it never occurred among them, though occasionally found in their joint aquatic abode at some little distance. But there the plants in question vegetated. The planaria panniculata receives ani- mal substances with less avidity than most other species, and seems more liable to de- cline in bulk, when removed to an apart- ment. Its proboscis is of singular length, and exactly trumpet-shaped at the extre- mity. Probably leaves are punctured by it to extract nutritious matter. This species is also akin to the former, 40 PLANARIA PANNICULATA. in propagating by eggs; from which, accord- ing to experiments made in the month of September, the young were excluded ex- actly in twenty-one days. The eggs are deposited on leaves; and the plexus of the common marsh iris prove a favourite receptacle, where the vicinity of the plant admits of it. These eggs are originally of a light colour, which speedily darkens with exposure, until becoming brown, but not so deep as that of the eggs of the black planaria. Applied to the micro- scope, each is discovered to be an exact ovoid, of the most perfect and regular fi- gure, with a smooth shining shell. I have not ascertained whether more than one is produced by an individual planaria; but the number of included young varies in differ- ent eggs, and they are, compared with others, of large dimensions at the moment of exclusion. Four young issued from one egg, while from another only a single animal, uncommonly large, was hatched. At first they are almost white to the naked eye; PLANARIA PANNICULATA. 41 nevertheless pinnate interanea are percep- tible by the microscope, which renders it probable that a nutritious substance is there received. The colour daily alters, and in the lapse of three weeks from their origin, some whose progressive increment had been studied, were changed to brown. About twenty marginal specks were visible in the earliest stage. ' The planaria panniculata is rather more inactive than the rest. Penetrating the folds and recesses of decaying vegetables, it lurks entire days in absolute immobility. In common with its kind, it is liable to the attack of a disease which always proves fa- tal, and extirpates numbers, almost before the observer becomes aware of its ravages. A swelling commences at the posterior ex- tremity, which rapidly ascends to the head, destroying the texture of every part in its advances; and the whole animal is sudden- ly resolved into a kind of whitish floccu- lent matter. 42 PLANARIA FELINA. Planaria Felina, Fig. 8. Hitherto our attention has principally been occupied by those facts in the general nature of plana- riz, which irresistibly obtrude themselves on observation; and although they cannot be denied singularity, they do not seem far removed from the common operations of animal physiology. Now, however, a spe- cies claims animadversion, possessing pecu- liar and exclusive properties, and such as are deemed anomalous in the ordinary features of Zoology. But let us not abuse the meaning of these expressions. It would be presumptuous to affirm, that what is ordina- ry in nature, is comprehended by the mind; or that what is of rare occurrence may not even be more easily susceptible of expla- nation. We are deluded by frequent ap- pearances into the belief of knowledge, and long before being able to reason satisfacto- rily concerning them, we are attracted to what is judged remarkable, merely because it has not been perpetually in view. In still or stagnant waters, for the most PLANARIA FELINA. AS part abounding with aquatic vegetables, and rarely in springs, there is found a dark brown planaria, of uniform colour, which at- tains considerable size. The largest which I have seen, were at least five-eighths of an inch in length, and somewhat less than one in breadth; but in general they are smaller, perhaps not above one in a thou- sand being of these dimensions. The co- lour is lighter than that of the panniculata, but some are of a dull, dark, dirty brown. The figure of the animal differs from that of the two former species ; therefore, if we are to found on slight external. discrepan- cies, a division of the genus may be made, including it, and others of similar organi- zation, particularly with regard to the specks or eyes. Bythis latter characteristic, it is dis- tinguished from the two subsequent species, to which it is allied by shape, and united to the two preceding. A short triangular tentaculum, or feeler, terminates each side of the head, susceptible of such contraction and dilatation, as absolutely to disappear or 4A PLANARIA FELINA. be extended to a point. When fully dis- played, the tentacula bear no imperfect re- semblance to the ears of a cat. The neck, which is narrower than the head, gradually enlarges downwards, until the extreme breadth of the animal is attained, and then a regular diminution ensues, terminating in a pointed tail. In the under surface, which is paler than the upper, one ventral pore can with difficulty be recognised; but the vicinity of an important organ, the probos- cis, is usually indicated by an elliptical spot, clearer than the general hue. By microscopical observation, or even with acute vision, here also a numerous row of jet black specks may be discovered, en- vironing the anterior margin, and proceed- ing about half down the body on either side. Their number varies in different in- dividuals ; sometimes they are nearly equi- distant, sometimes irregularly arranged, or two appear quite close, and almost con- founded together. I have counted between thirty and forty in several; and the margin PLANARIA FELINA. 45 of a very minute planaria, subjected to the microscope, disclosed twenty-four. The real purpose of these characteristics, I have not been more successful in establishing, than their use in other species. But it may, perhaps, be less difficult to institute a series of experiments with that view on the felina, than on those planarize where they are not equally conspicuous. Protected by its native element, the pla- naria felina reposes inactive on the inner surface of aquatic plants, on fragments of decaying wood, or the under part of stones. {t can with difficulty be dislodged from crevices where it takes up its abode, per- tinaciously adhering to different substan- ces, until removed by a soft feather, or washed off by repeated immersion in wa- ter. The societies in which it lives, in-. clude those of every age; and should the fluid containing them accidentally evapo- rate, all appear crowded together, contract- ed into a small regular ellipse. If a num- ber be confined in a glass vessel, the whole 46 PLANARIA FELINA. assemble in a quiescent state, on the side next the light.. Some others, which natu- ralists have classed in the genus, repose on the side opposite the light ;—so decided are the characters which regulate the dis- position of animals. This planaria, like the rest of its genus, is powerfully excited to motion by the pre- sence of light. Then it traverses the sides of its glass with a lively gliding progres- sion, or swims supine at the surface of the water ; but neither it, nor any which I have seen, except the flexilis, ventures to com- mit itself entirely to that element. If dropping from the surface to the bottom, which is a characteristic of all this and the next division of the genus, it seems to ex- ercise a faculty belonging to the caterpillar, of spinning a silken thread, visible only when so much aggregated as to interrupt the rays of light. Its use is evidently to check the rapidity of descent ; and a com- plete view of its effect may be obtained by including a plant of Veronica, crowded with PLANARIA FELINA. 4:7 planarize, within a tall glass jar. Their nu- merous descents from the upper leaves, quickly form a perceptible column, owing to the infinity of glutinous or silken lines. The animal being extremely sensible of cold, a considerable temperature is requi- red to promote its activity. On the se- venth of August 1812, though the thermo- meter in the heat of the day stood at 62°, a certain chilness from a breeze at east per- vaded the air, which led planariz to retreat under stones for shelter. The mucilaginous part of decaying ve- getables probably constitutes the ordinary food of this species ; but animal substances are also voraciously consumed, especially the soft and bloody portions. . Mussels and oysters are peculiarly grateful; and after feeding copiously, the whole body of the planaria rises from a flattened form almost into a semi-cylindrical shape. In this con- dition, its various proportions are best ex- posed, in consequence of the universal or- ganization being expanded. Sometimes, 48 PLANARIA FELINA. in conformity with others, it refuses food for weeks, and then receives it with avidity. However, its usual readiness to feed, ren- ders it the most favourable subject of all for experiment and observation. } These circumstances, which are a sulle! cient guide to recognition of the animal, being premised, we have next to consider certain admirable phenomena by which it is more eminently distinguished. Though I have possessed hundreds of id planaria felina at every season of the year, I am ignorant whether its propagation re- sults from the sexual union, and whether it multiplies by eggs or living foetuses. I have anxiously investigated the point; but no experiments have had a satisfactory is- sue, nor has any circumstance whatever, either immediate or remote, tended to the most distant elucidation of it. Once, in- deed, I thought that some minute, whitish, elliptical bodies, which afterwards disap- peared, were discernible at the bottom of a vessel in October 1811. Nothing followed, PLANARIA FELINA. 49 however, and the like never recurred. Yet I confess myself inclined to believe that these planariz are perpetuated by eggs, notwithstanding I have not been for- - tunate enough to obtain the parent animals at the proper period, or to seize the mo- ment of production. On removing: a quantity of plants fre- quented by this species into a glass jar, and filling it with water, the observer will soon discover many planarize, complete and per- fect in all their parts, vivaciously traversing the sides of the vessel. But others he will also distinguish, exhibiting strange and un- seemly mutilations. The tip of the tail, or a large portion of the body, is wanting; the . structure of the head itself is impaired ; distorted stumps are united to regular or- gans, and the colour of one part apparently denies its continuity with another. In re- peating his examination, the observer will next find several shapeless fragments, un- like any thing he has previously beheld, adhering motionless to the bottom and sides E 50 PLANARIA FELINA. of the glass; and although he watches them whole days, he will scarce be sensible of their animation. The defective confi- guration of the animals bears so little rela- tion to those entire, as to afford strong grounds for doubting their identity with the species; and, assuredly, except in the general hue, in the similarity of motion, and in a triangular head armed with tenta- cula, scarce the faintest resemblance exists. All this, however, is the consequence of an important operation, by which nature is en- gaged in perpetuating the race. Sponta- neous division of the body has taken place; each separated portion is in its progress to perfection as a complete animal, and either — extremity is in the course of repairing what it has lost. The majority of the mollusca tribe, per- haps the whole with which we are acquaint- ed, as also the numerous vermicular race, propagate only at certain seasons of the year, and most commonly after the sum- mer heats have declined. But the spon- PLANARIA FELINA. Sil taneous separation of parts ensues at all times with these planariz; in every si- tuation, and indifferently, whether the in- dividuals be large or small. Having con- fined four on the third of November 1810, I remarked on the ninth and tenth, that two of them had lost a fragment at the ex- tremity of the tail. Some were taken on the thirteenth of January 1811, which, about a week afterwards, shewed defective organs. Numerous spontaneous divisions appeared among those removed from the waters during the September succeeding ; and an opportunity occurred of remarking the like throughout the month of August 1812. There seems no exact rule or limitation, in respect to the quantity separating. Sometimes it is a minute fragment ; some- times as much as leaves the proboscis ex- posed, or towards a third of the body. The largest portions are always heart-shaped, and opaque, both from size and consistence; thus obscuring the interior, if any thing 1s 52 FLANARIA FELINA. there to be discovered. A portion delinea- ted soon after separation, is represented somewhat magnified, Fig. 9. which, sub- sequently, became a. perfect animal. But the paleness of the lower extremity denotes that a previous disjunction, though then completely repaired, had taken place. A- mong those observed in August, one had lost the head, either by accident or sponta- neous division: while an oblique section had. carried away nearly the whole anterior part of another. Only the point of a ten- taculum remained. From this and various examples better illustrated, separation is not peculiar to the posterior extremity. It can as little be ascertained that there is any previous preparation for division. No in- dications are betrayed; and in so far as I have witnessed, it takes place just as an or- dinary incident in the animal’s existence. But there is a material difference in the consequent state of the two severed por- tions. The anterior part scarce seems to suffer from its loss; while the fragment PLANARIA FELINA. 53 _disjoined is condemned to absolute quies- cence. The life, habits, and motion of the former, are unimpaired; whereas nothing, unless a painful sensation, can stimulate the latter to a mere change of position. Its animation is as if suspended, until the defective organs be renewed. When in- specting one of these animals on a summer evening, I saw the head separate from the body, without any apparent struggle, and crawl away. And at another time, when exhibiting to a friend the remarkable mode in which the creature feeds, a portion of the tail was detached, while in the act of simple extension. The remainder did not seem in the least affected; and the suste- nance provided was readily received. It must be admitted, however, that more ri- gid observation might discern some obscure anticipation of division, though such has not fallen under my notice. Notwithstanding the absolute quiescence of the severed fragment, an essential pro- cess is going on. From the moment of se- 54 PLANARIA FELINA. paration, a new head prepares to vegetate from before; and all the subordinate organs are successively developed. But during its advances to perfection, this regenerating animal cannot be known to pertain to its proper species; and on slight, nay, on at- tentive inspection, no one would hesitate in pronouncing it different. The vacuity that formed the recess of the heart is soon filled up by a reproducing substance, from which a clear light-coloured papilla next arises, and gradually protrudes into a long slender organ, while the general shape and size of the original fragment are re- tained. Thus a clumsy and distorted ani- mal is presented, equally remote from the parent whole, from the portion detached, and from the figure which it will ultimately attain. But in progress of time, the dia- meter of the body decreases; the regene- rating protrusion is enlarged ; its extremity. is fashioned into a head ; the eyes and ten- tacula appear; all the parts are bounded by a regular outline ;—a perfect animal is PLANARIA FELINA. 58 produced. Such, in few words, is the mode in which the simple renewal of organs is ac- complished. Along with their redintegra- tion, quiescence is abandoned, the necessi- ties of the creature return; it vivaciously traverses its element, alternately feeds and reposes, and at length exhibits every pro- perty of the entire animal, whereof it so lately formed a shapeless fragment. Again it must, in its turn, lose a portion, which undergoes similar transitions from immobi- lity to action, from rudeness to perfection; and then, what originally constituted part of the organization of the parent, is trans- muted into two complete and entire ani- mals. In regard to the mutilated trunk, a simi- lar operation, though marked by fewer sin- gularities, is going on. The wound heals ; a prominence buds forth, which, by de- grees, is prolonged into a well-defined re- gular tail, of lighter colour than the rest of the body. The reproduction is fulfilled, and the animal resumes its integrity. 56 PLANARIA FELINA, This kind of regeneration seems univer- sally diffused among the species; most of those, removed from their native abode, un- equivocally shew the acquisition of the pos- terior extremity. But these facts merit more explicit detail. On.-the tenth of November 1810, a small fragment was detached from the tail of each of two planariz. Next day, as sometimes happens, they had removed from the spot of separation, to await in quiescence the ex- ercise of their reproductive powers: which were not slow of being unfolded. On the twenty-second of the month, both had ac- quired complete heads, and were vigorous- ly traversing every part of their element ; though still very small, being hardly one- fifth of the size of the original animals. The regeneration of each defective trunk was likewise now so fully accomplished, that it could with difficulty be known which of the planariz, compared with others, had lost the fragments. The new animals had at that time resumed their 4 PLANARIA FELINA. 57 pristine motion ; but their figure had none of its proper proportions; nor was it before thestwenty-eighth of November, or eigh- teen days from, separation, that it could be called regular and well defined, and resem- bling the shape of unmutilated planarize. Their size was always inconsiderable ; and if ever a portion thus sundered by the hand of Nature grows as large as the trunk which has lost it, I can affirm that it is not in a state of confinement. Probably a fragment successively sepa- rates as the new tail is completed; a fact which deserves investigation, as elucidating the great extent of generation by sponta- neous division. The mutilated trunk seems as well adapted for reproduction after lo- sing its extremity, as when entire. Many may perhaps conceive, that the defective organs exist in miniature in the severed portions ; and that dissection, aid- ed by powerful magnifiers, might bring them into view. It would be hardy to maintain an opposite doctrine ; for extreme 58 PLANARIA FELINA. delicacy in separating the component parts, and the nicest observation in other cases, have detected those rudiments of organiza- tion, which are wont to be exposed only in the perfect state. Here the like evolution succeeds; but the experiment seems be- yond human ability. | Microscopical obser- vation discovers nothing more in the sepa- rated fragments, than what unassisted vi- sion has seen. There is no indication of specks or tentacula: no symptom of an aperture for the protrusion of the future proboscis. The anterior not being reduced to an edge, remains of considerable thiek- ness; it is smooth, even, and resembles a piece of flesh divided by a sharp knife. It has before been explained, that all ani- mal reproductions being materially influen- ced by the heat of the atmosphere, the re- newal of defective parts is accelerated or retarded accordingly. Some fragments, therefore, are perfected earlier than others ; but increment advances even where the temperature is low. It would be interest- PLANARIA FELINA, 59 ng to institute a series of experiments, for the purpose of ascertaining the relative progress of regeneration, during a variety in the permanence of temperature. Is every kind of vegetation, both in plants and animals, accomplished by the same quan- tum of heat, though unequally distributed with respect to time? Will 800° applied in ten days, at the rate of 80° daily, haye the like effect in renewing the defective organs of a planaria, as 800° continued for twenty days, at the rate of 40°? Two points would necessarily be kept in view; first, the degree of cold when vegetation cannot advance; secondly, the degree of heat injurious to the species. It appears to me, that planarize soon begin to suffer. One which had been exposed to the heat of 99° survived; but higher degrees seem fatal. The success of the experiment would thus depend on chusing a proper medium. If this be the sole and natural mode of propagation among planariz, it presents a 60 PLANARIA FELINA. phenomenon in the history of the animal creation. I have, as already said, kept hundreds of the species in question, at eve- ry season of the year, and subject to almost every condition, yet none other has at any time been witnessed; and, so far as my observations go, no individuals are ex- empt from dismemberment of the body. It succeeds alike in the large and small, whe- ther abstinence or repletion prevails; and as well with those extenuated, as when co- piously supplied with nutriment ; in a state of liberty, and one of confinement. Still, this is not enough to deny, that the race may be also perpetuated by the ordinary means which nature has chosen for the pre- servation of animals. Possibly the fact is already proved by authors, with whose works I am unacquainted. The knowlecdJe of man is scanty; his understanding is im- perfect: and the humble ‘enquiries of one may long be directed in vain, to what the more brilliant talents of another conquer without difficulty. PLANARIA FELINA. 61 Propagation by spontaneous division into parts, and the subsequent evolution of want- ing organs, are not altogether unexampled. Among creatures which almost elude hu- man research, the Animalculz of infusions, there are certain species that partition asunder, and each of two severed portions’ quickly becomes a perfect whole. Others separating into more numerous parts, give birth to so many animals resembling them- selves; and the young of the polypus buds like a scion from its mother’s side. But observations on the progress of animalcular generation are embarrassing to the physio- logist. He must resort to the highest mag- nifiers to reach what his simple vision can- not penetrate; and he will too often feel dissatisfaction instead of confidence from his investigations. ‘The nascent polypus is not independent of its parent; its suste- nance is thence derived ; its locomotion. is the result of will in common; and its in- corporation is complete, until expanding organs admit of separation. Here, on the 62 PLANARIA FELINA. contrary, spontaneous division succeeds in animals, a thousand, nay, a million times exceeding the inhabitants of infusions in size; of which the parts and proportions being visible to the naked eye, contribute to the dissipation of doubts, and display in ‘detail the progress of regeneration. Be- sides, the severed portion, condemned to quiescence, and destitute of alimentary or- gans, survives independent of the mutilated trunk, until their evolution follows by the regular and gradual operation of nature. Such remarkable phenomena, incessantly offered to my notice, afforded ample scope for speculation. If these animals, I began to reflect, be endowed with so powerful a reproductive principle, it is not impossible that some singular and interesting -monstro- sities may be obtained by artificial means ; and my confidence in its practicability was corroborated, by having occasionally found deviations from the ordinary figure in the natural state. One of those was truly won- derful. The planaria itself, in relation to PLANARIA FELINA. 63 others, was of small size; its tail was bifid, and out of the cleft grew a body, quite se- parate and distinct from the main trunk of the animal, and preserving an erect pos- ture, while the two tails were applied to the plane of position below. In reasoning from simple appearances, two conclusions might be deduced : first, that the posterior extre- mity of this planaria had been accidentally cleft into three parts, but all having sepa- rated by spontaneous division, only two were renewed by the ordinary course of re- production ; and the third, situate between them, had, by some strange and anomalous process, been developed into a body, sur- mounted by a head, smaller than the princi- pal body, indeed, but lively and well defined. Secondly, if the parts had not been cleft asun- _ der by accident, so as to give birth to this inexplicable renewal, the peculiarity could probably be ascribed to an original mon- strous conformation of the germ, or foetus, whether expanding in an egg or in the bo- 64 PLANARIA FELINA. dy of the parent, if such modes of propaga- tion belong to planariz. Unequivocal symptoms demonstrated, that the inclinations of the superfluous head were not always in unison with those of the remainder of the animal ; that it pre- ferred quiescence, when they chose motion; and that it would willingly have traversed _its element, could its strength have predo- minated over the inactivity of the major parts. In subjecting this planaria to the micro- scope, the preceding phenomena were still more clearly illustrated. Numerous black specks, the supposed eyes, or spiracula, ap-_ peared surrounding the larger head; some were disseminated over the upper surface ; and they environed the margin of the small- er head also. In the course of a week, or little more, after the planaria had been taken, which was in the heat of summer, the posterior head had separated by spontaneous division from the principal body, and had disappear- 1 PLANARIA FELINA. 65 ed. But soon afterwards, a kind of projec- tion occupied its place; and it was not with- out amazement, that I beheld this projec- tion vegetate into a new head, resembling the one which had been lost. About a month having elapsed, it was well shaped and en- tire; marginal specks were perceptible by the aid of the microscope; and, like its pre- cursor, it shewed a tendency to motions different from those of the rest of the body. In about three weeks more, this secondary trunk was so large, as to constitute rather above a third of what an animal of corre- sponding proportions, in the natural state, should have been. Then, instead of follow- ing its ownwill by crawling along the bottom of the including vessel, it was frequently seen bending in a curve over the plane of position, while carried along with the other parts, whose propensities it was incapable of resisting. The monster now described, having thus been provided with three different heads, fed copiously, and lived several months in ¥ 66 PLANARIA FELINA. my possession. Its reproductions are par- ticularly to be admired, because I observed one of the same species, with a bifid tail, lose both parts by spontaneous division; and although each fragment acquired a new head, and became perfect in its kind, the mutilated trunk regenerated only a single new extremity. These circumstances contributed still fur- ther to corroborate my belief in the proba- ble effect of experiment. They proved that superfluous organs, however they origina- ted, might exist, without injury to plana- riz. Therefore, if separating parts became complete animals; if a mutilated trunk re- gained the defective portion; and if a head, the most important of all organs, was evol- ved from every inconsiderable fragment, it was reasonable to conclude, that, by some particular operation, supernumerary parts might be produced. Yet it was long be- fore reiterated trials were rewarded with success, and I had almost determined to abandon the enquiry, conceiving that a cer- PLANARIA FELINA. 67 tain nicety, of which I was not master, should be practised: and that it had been beyond my ability to detect the secret cause of failure. But the powerful reproductive principle which continually vegetates upwards, the invariable acquisition of a head by the neck from which it is severed, added to a similar production in spontaneous division, gave ground for conjecture, that if part only of an incision healed, some generation still upwards would ensue. On the other hand, should the whole incision heal, matters would remain entire. It was also most likely, that the regenerating portion would become a head, and that more than one might thus be produced on the same ani- mal. | With this view, an incision, considerably lower than the head, was. made in three planariz, on the twenty-eighth of Sep- tember. It completely healed in two, and the animals appeared almost as if untouch- ed. One of them survived above a year, 68 PLANARIA FELINA. when nothing except the slightest indica- tion of a scar was perceptible. But with regard to the third, it was evident, after a certain period, that the lower part of the incision had not healed, as in the others. An unnatural prominence interrupted the general contour of the side, which continued protruding into something unlike any or- ganization peculiar to planariz. Its pro- gress advanced; the outline was more and more impaired, and at length, about the twenty-fifth of October, nearly four weeks after the operation, the superfluous repro- duction was clearly recognized to be the rudiments of a new head. The order of the experiment, however, was now disturb- ed; for the original head had separated close to the neck, by spontaneous division, and remained independent of it. A doubt might thence have arose,—would the new and superfluous organ springing from the under part of the incision, supply the place of that which had just been lost, or would a head, the third in number, including the PLANARIA FELINA. 69 one artificially produced, vegetate from the mutilated neck, to restore the integrity of the planaria? I certainly did anticipate that such would be the case, because the principal end of reproduction is to repair wanting parts, that the animal economy may be preserved entire; and so in fact it happened. | On the eighteenth of November, the operation of Nature was fully accomplish- ed; a new and perfect body, crowned by a head, had grown out of the side of the pa- rent animal, distant about two-thirds of the total length from the extremity of the tail. Marginal specks, the eyes or spiracula, were quite perceptible on the twenty-se- cond; the superfluous organization was complete and well defined, and its incre- ment continued still advancing. Though provided with only one proboscis, both bo- dies were immediately enlarged by the ab- sorption of food, which plainly proved nu- tritious. | I could not contemplate this creature 7O PLANARIA FELINA. without admiration, heightened, perhaps, by the difficulties that had been surmount- ed in its production. The order of nature had been disturbed; something which was not essential to preserve the animal func- tions had been generated ; and a being now appeared, to whose existence the laws of organization were adverse. Reproduc- tions are permitted, indeed, to some fa- voured animals; but they are only for the purpose of supplying parts originally perfect, and they seldom, if ever, attain the utmost limits at first assigned. As supernumerary organs are unnecessary in fulfilling the ends of creation, it may be conjectured, that they can never appear without some mal- conformation in the rudiments of an ani- mal; from some violence, which displaces one part, represses its expansion, or ad- mits its union with another; and the same may be accomplished by the injuries of dis- ease. Here the planaria first lost its head by spontaneous division, a phenomenon pe- culiar to the race; next a new one had PLANARIA FELINA. val been evolved from an incision in the side; and lastly, though this would have restored the integrity of the animal, the separated head was replaced by that law which ordains the renewal of a wanting part. Though the sensorium of the animal world be more pre-eminently distinguished in the head, we cannot altogether reject its universal diffusion, to a certain degree, throughout the body. What was before remarked, concerning the different condi- tion between a separating fragment and the trunk it had left provided with a head, probably establishes the residence of the sensorium, however low in quality, proper to planariz. The truth was forcibly im- pressed by the propensities of this double- headed animal, coinciding with those of the monster already described. Sometimes when the body was in motion, the new or- gan advanced as if in willing participation : but on other occasions, it was reluctantly dragged along. Then, instead of preser- ving the same direction as the rest, it bent 2 PLANARIA FELINA. into a curve, and abandoned the plane of position. Yet it was always subservient to what properly constituted the parent whole; that being the consequence of its subordi- nate size. In the subsequent months of December and January, the three portions composing the total animal, namely, the two heads and the tail, were nearly of equal length, which created no little embarrassment in its pro- gression. When the inclinations of any two were in unison, they overpowered the resistance of the third, which could only disturb the regularity of their course. Experiments of a similar description ha- ving been repeated on the thirtieth of Octo- ber 1811, several years after my attention had been first directed to the subject, they proved abortive for the most part, or the pla- narize perished. But on the twenty-fourth of November, I observed a minute head vegetating from the side of each of two that survived. One inclined considerably down- wards, in the direction of the tail; the an- PLANARIA FELINA. 73 terior angle formed by the body, or rather between the bodies of the other, was more acute. The relation of the generating parts, nevertheless, always gained greater uniformity with the general outline and fi- gure of a planaria in the natural state. As their dimensions continued to enlarge, their action became more lively and distinct, and soon corresponded with the external pro- perties of an entire unmutilated animal. A head thus protruding from the left side of a planaria artificially rendered monstrous, ‘ is represented, according to its real incre- ment on the tenth of December, or about six weeks after the operation, Fig. 10. Its growth, it is true, continued long after- _ wards, and until very nearly equalling the size of its fellow; but the apprehension of accident, to which the tender substance of such creatures is so much exposed, induced me to obtain this premature delineation. It is therefore proved beyond controver- sy, that an incision in the side of the plana- ria felina, executed in a particular manner, 74: PLANARIA FELINA. will generally, if not invariably, give birth to a new and additional body, which, in progress of time, approaches the dimensions of the integral animal, and exhibits the same functions and properties by which it is distinguished. Where the chief object has a partial fai- lure, other gradations of monstrosity are un- folded, which undergo successive altera- tions. In watching the result of an expe- riment, I saw two rude and mis-shapen heads, united close by the neck, protrude from asevered fragment, which had once constituted the posterior part of a_pla- naria. The fragment bore an imperfect resemblance to a circular arc; whence its motion, instead of being in a direct line, described irregular curves. Five weeks af- ter this remark, the regeneration of the two heads, still in intimate union, was com- pleted, but the distortion of the body re- mained. However, a greater interval ha- ving elapsed, the whole grew into shape. The two heads were then seen farther apart: PLANARIA FELINA. 15 each had acquired a longer neck; the body was taper and well-defined, pursuing a smooth and gliding progression, like that of a planaria which had never suffered mu- tilation. Hitherto the source of generation has been veiled in impenetrable mystery. The universe changes its tenants in endless suc- cession: scarce is the parent mature, when it is supplanted by its offspring, and still the origin of both is lost in obscurity. No lucid reasoning aids the philosopher; no de- licacy of experiment leads to conviction. Nature seems to have willed, that the means by which animation is excited, preserved, and transmitted, shall not be disclosed. But is it wonderful, that the vigorous industry of the human mind should have been so unsuccessful here? Let us remember that the most ordinary incidents, those of con- stant recurrence, and which are ever pa- tent to view, remain unexplained, or that an ill-judged anxiety has substituted con- jecture for truth. "6 FLANARIA FELINA. Our difficulties are not lessened by the phenomena which just have been exposed. Whence does it follow, that when either an accidental or an artificial incision in the side of a planaria is sufficiently large, a su-_ perfluous body must shoot forth, while, if the lacerated parts approach, those organs, which would have protruded, to become se- parate and distinct, are merged in the ge- neral whole? Is there a universal diffusion of germs, or the elementary principles of li- ving matter always in readiness for deve- lopement, each moment that opportunity shall admit? Yet nature does seem to la- bour more, and her powers to experience greater difficulty, in accomplishing this kind of reproduction, than in the renewal of or- gans lost by spontaneous separation. Ap- parently, few conditions are requisite for the one; it is enough that the division have taken place, and that a certain temperature of the atmosphere shall succeed: but for the other, some essential and secret quali- ty 1s indispensible, to which we know that - PLANARIA FELINA. wy, the union of the lacerated parts will prove fatal. ‘To the rest there is no clue what- ever. In simple privation of the head, we are more easily reconciled to conjectures on the cause of it being replaced, from the efforts of nature to supply a defective part; but it is difficult to com prehend, why, in experiments for the production of super- fluous organs, it is only the anterior, and never the posterior portion which protrudes, that the upper division of the laceration produces nothing. In pursuing these remarks, we may af- firm, that there is perhaps a certain poimt of the body where a head ceases to vege- tate upwards, and whence a tail will vege- tate down. It would be interesting to as- certain where that point is placed, and whe- ther it may not be connected with some organic structure, which will tend to eluci- date the cause of monstrosities. My own experiments regarding the fact have not been conclusive; probably from being too few in number, or too little diversified. A 48 PLANARIA FELINA. prominence growing from the side of a pla- naria a long time, that 1s, months after an operation, resembled the stump of a tail. The termination was acute, and there were no tentacula, by which the anterior is al- ways characterised; but marginal specks, which, if regular, also distinguish the head, appeared, and its movements were more active than belongs to the subservient qui- escence of the lower extremity. Thus it was seen on the eighth of February, while it was a mere stump on the first of December preceding. Perhaps the opera- tion here took place very near the spot from whence either a head or a tail would pro- ceed; or almost in that manner which may give birth to either. However, had the animal lived, I was induced to think, that the more probable issue would have been the former ; consequently, that the incision was somewhat higher than the position of the point in question. I remember, that after another experi- ment made on the twenty-eighth of Sep- PLANARIA FELINA. 79 tember, a projection perceptibly vegetated from the side of a planaria in the end of the subsequent month. The animal fed abun- dantly, and on the tenth of December I was sensible that it was about to become a head. These reproductions of uncertain issue are longer of demonstrating their real charac- ter, than those which, from an early stage, leave no opportunity for doubt: the one is completed before the other assumes its leading features. They are not totally de- pendent on the art of the experimentalist; though examples in the natural state are extremely rare. In the first week of Au- gust 1812, I took a number of planariz. Some time afterwards, my attention was attracted by the protrusion of an organic substance from within about a third of the posterior extremity of one of them, which, as it enlarged, exhibited active motions and inclinations, resembling those, as in the for- mer case, proper to the anterior portion. Circumstances compelled me to abandon my observations, by which I was then led to 0 80 PLANARIA FELINA. conjecture, that the production would be analogous to a head. Such regenerations, for the most part, bear a general cast and appearance which guide to anticipations of their ultimate issue, and my belief wasfound- ed on what I had previously beheld ; for al- though analogical reasoning is not to be trusted, if single and unsupported, still, when combined with a series of facts, all uniform, clear, and distinct, it is impossible to reject it in our conclusions of events. Being unex- pectedly enabled to resume inspection of the planaria now alluded to, I discovered that my conjecture had not been altogether falla- cious. The origin of the protrusion on the eighth of September was rather more than half way down the side; the whole anterior part was surrounded by specks or stigmata, and still greater activity testified in its movements. Nature was evidently labour- ing in the production of a head, though tentacula were wanting: and if another un- seasonable interruption had not taken place ‘on the fifteenth of the same month, I should PLANARIA FELINA. 8] probably soon have witnessed the further advance of that organ to perfection. It is thence to be concluded, that where- ever a strong tendency to action is display- ed by a shapeless reproduction or vegeta- tion from an entire planaria, an organ, the most important to all animals, the head, will finally be developed. Doubts frequently occurred, whether a duplication of the tail would invariably be produced by an incision towards its extre- mity. Notwithstanding such seems to be the general law of nature, anomalies here bewilder the observer. In one planaria, the portion generated was much longer than the original tail ; it was endowed with more activity than is peculiar to that organ, and, as in the former instance, its motions had greater similarity to those of a head. No marginal specks appeared. Another experiment of this kind was made on the twenty-seventh of November 1811. A new extremity accordingly protruded; but about the eleventh of February 1812, the origi- G 8g PLANARIA FELINA. nal tail separated by spontaneous division. It might have been expected, that the other, which seemed capable of fulfilling all the organic functions, would have effected the purposes of nature; nevertheless a re- production of the first extremity ensued. A monstrosity of a very extraordinary kind occurred just about the close of my whole observations on planariz. On the thirtieth of March, I took between thirty and forty of the species, two of which ex- hibited some peculiarity at the very termi- nation of the tail; there seemed to be an unnatural redundance of organization. A few days after, on inspecting one of them, I was surprised to see this deformity con- sist of a minute animal, in progress to com- plete regeneration, attached to the extre- mity by a slender ligament. Its head was pale, not perfectly shaped, but the margi- nal specks were perceptible ; and its posi- tion, when at freedom, was almost at right angles to the larger planaria. How had the creature been formed? Probably an PLANARIA FELINA., 83 accidental injury had severed a fragment of the original tail from the body, all ex- cept the slight ligament by which the nas- cent planaria was now connected to it. The reproductive operation ensued ; a new head vegetated from the anterior part ; while the clearness of the tail of the larger animal proved it to have regenerated from a wound. In time, however, and as the young planaria gained greater strength, it was to be anticipated, that its forcible ad- hesion to the plane of position would tear asunder the ligament. Its shape was near- ly entire on the ninth of April, and it had visibly begun to exert that faculty. The second monstrosity consisted of a planaria, whose posterior extremity terminated in another smaller animal, united at right an- gles to it, and what seemed the tail of the latter protruded from the right side: thus the larger planaria, properly speaking, had no tail, or it merged in the body of the other. The source of monstrosity is an abstruse 84 PLANARIA FELINA. and difficult enquiry ; less so, however, in endeavouring to understand how the origi- - nal superfluities or imperfections of orga- nization appear, than the subsequent re- dundancy of parts. Assuming that the elements of the future animal pre-exist fecundation, and are perfect, it is more easy to comprehend how excoriations in an early stage of life may admit such a union from the powerful tendency of animated matter to vegetation, as to produce mon- strosity by excess; and as the whole aber- rations of nature are perhaps reducible to two divisions only, we can in like manner conjecture how an injury to some unfold-. ing organic principle shall repress its com- pletion, and occasion monstrosity by defect. We can also ascribe the renewal of parts to that law which strives to maintain the inte- grity of an animal, and preserve to it the means of carrying on functions necessary ~ to its existence, though it be unaccountable why the reproduction never exceeds the proper limits. PLANARIA ARETHUSA. 85 All this, however, will prove of little as- sistance in explaining how monstrosities by excess are artificially produced, while we should rather conclude that they ought to terminate in defect. Planaria Arethusa, Fig. 11, 12, 13, 14. Naturalists have affirmed that some plana- riz are entirely destitute of any semblance to eyes; an opinion which, in one well- known species, we have proved to be falla- cious, and possibly it might be found equally so respecting all others, or almost all, were they rigorously examined. Reflecting on the transcendant privileges which a sense of inestimable value confers, we shall cease to wonder at the solicitude of physiologists to ascertain whether it has been dispensed with in the structure of the smaller ani- mals. But there are various planarize whose vi- sual organs are better characterised, both in site and appearance, than by clusters of specks on the upper surface, as in the Flex- 86 PLANARIA ARETHUSA. ilis, or by their numerous dispersion singly around the margin of the Nigra, Pannicu- lata, or Felina. Two specks, as if in orbits, occupying the middle of the neck, or four distributed in a regular quadrangle in the vicinity of the head, seem to denote a spe- cial purpose relative to external objects. In nothing is there greater diversity than in the disposal, power, and faculties of the organs of vision among the inhabitants of the air, the earth, or the waters. They are adapted either to aid the discovery and capture of prey, to shun the enemies of the race, or to that peculiar medium in which their natural dwelling has been assigned. In the years 1802 and 1803, a planaria occurred to me of this description, which was then the subject of diversified experiments. But when desirous of repeating them more recently, I found that it had altogether dis- appeared from its wonted abode; and being unable to discover it elsewhere, a section, once designed for its history as the planaria rufa, shall now be suppressed, especially as PLANARIA ARETHUSA. 87 no delineation of it was obtained at the time. I may just observe, that in figure, colour, and position of the eyes, it seemed closely allied to the Planaria auriculata of Muller, described and represented in the Zoologia Danica, vol. li. page 37. Plate Ixviii. Figs. 16,17. The latter, however, was scarcely perceptible by the naked eye, and an inhabitant of the sea; whereas mine dwelt in fresh water, and nearly approach- ed the former species in size. The sudden disappearance of animals without any sensible cause, is not unexam- pled. I have witnessed it myself among the smaller tribes; and the same is record- ed by the most celebrated naturalists. There are reiterated proofs that those of gigantic proportions have become extinct ; and it is probable that others are daily vanishing from the surface of the earth, which none excepting hybrids can be said to replace. Several sources, equally effectual, may con- tribute to the extirpation of animals; the preponderance of enemies, cessation of the she 88 PLANARIA ARETHUSA. accustomed food, or the ravages of disease ; and it is not unlikely that some fatal at- tack, such as that which resolves the pla- naria panniculata into a flocculent sub- stance, has eradicated many of the kindred species. In three pure springs, and also at-the bursting of a very faint discharge from the ground, I have obtained a planaria in certain respects analogous, which I never observed in stagnant waters. Above, it is generally of a leaden grey, deeper in proportion to its size; the under part is pale, with a line of different hue, proceeding from the origin of the head to within a third of the oppo- site extremity, which denotes the site of a large intestine. Its figure is more slender and delicate than that of any of the other fresh water species here described ; flattish like them when in a state of abstinence, and forming the segment of a cylinder if feed- ing copiously. It is about half an inch long, and the twelfth part of an inch in breadth ; PLANARIA ARETHUSA. ; 89 and is further characterised by being pro- vided with two eyes. On the seventeenth of September 1809, { took between twenty and thirty of these animals, the larger four or five lines in length, and of the usual colour; but the smaller of a lighter shade, and some even whitish. The diversity of hue excited em- barrassment concerning the identity of the latter with the species: Nor was this re- moved by taking a number of the same planarize, in the course of the succeeding year, among which were several almost white, though exactly similar to the rest in size and proportions, while they were too large to be considered young. Further observations have shewn, that there is lit- tle restriction with respect. to size, some being seen thus distinguished, which, if not equal to the largest, are scarce infe- rior to them; and it yet remains to be ex- plained, whether the paleness be acciden- tal, whether it characterises an additional species, or only a variety. I am rather 90 PLANARIA ARETHUSA. disposed to condescend on the last, and to lay down, that the leading species is always grey in its original abode, and darker as it is larger. Very fine specimens of both inhabit a spring at the north-west base of the rock surmounted by the castle of Edin- burgh, close to its issue from a ruin called the Well-house Tower. I have also, but rarely, found a planaria almost exactly of the same description as what is denominated the leading species, except in being of deeper grey, the body somewhat of a more slender, equal, and vermicular form, the tentacula less promi- nent, and the head broader at the extre- mity. The frequency of the animal has not been sufficient, nor the distinctions so evident, as to enable me to prove whether it is a variety, or should be disjoined from the species. Possibly such discrepancies may originate in sparing aliment, the ab- sence of light, or the temperature of the at- mosphere. It is inconceivable on how many conditions the real external aspect of these PLANARIA ARETHUSA. 91 animals depends; the mere passing of a cloud before the sun will produce so ma- terial and sudden an effect, that a total change in shape and motion, consequently in colour, ensues. Nor is it difficult to comprehend that it must be so, by reflect- ing on the extreme dilatability and con- tractility with which every portion of a planaria is endowed; that in progression its length is at least quadruple as much as when at rest; that its tentacula can disap- pear at will, and that the whole proportions of its body can be changed. Want or abun- dance of food will occasion analogous altera- tions in colour, size, and figure; new ap- proximation or separation of parts arises, and the animal is hardly seen twice identi- cally the same in every thing. Repeated observation is therefore the sole means of appreciating the relation of all these com- binations. In searching for the permanent charac- teristics which might distinguish the pla- nariz now described, I subjected two of 99 PLANARIA ARETHUSA. pale colour, selected from the rest, to the microscope by candle light. Nothing re- sembling eyes, stigmata, or marginal specks, could be detected. At a future period, however, on repeating the investigation by day, two minute black specks were disco- vered in the middle of the upper surface of the neck, nearly in the same position as they are to be seen in the planaria auriculata. _ This is an observation, like some others on animals which elude our controul, exceed- ingly difficult to be accomplished, both from the corporeal opacity and incessant motion of the planarize ; and in those of dark co- four, it is scarce possible by any means to obtain a view of the eyes. Whether they are simple or compound, is not absolutely certain. More probably each is a single speck, deep sunk in an orbit or socket, where perhaps it is susceptible of some movement or alteration of figure. They appeared differently in different observa- tions. Both were not.always of the same shape; frequently they resembled a cres- PLANARIA ARETHUSA. 93 cent, and by a constriction in the middle, occasionally seemed almost divided asun- der. Their position appears ‘in Fig. 13. which represents one of the pale animals somewhat magnified. An instance occur- red, where, by a monstrous conformation of the head, a planaria had a third eye situa- ted to the right of the other two. The organ of vision, if it be truly such, is not the only one whose site or opera- tion is obscure in planariz. I had studied the history of several species of this tribe during successive years, without being able to discover the precise manner in which they fed, though repeated experiments were made for that purpose. But I cannot deny my having been partly misled by the authority of nomenclators, who, founding their conclusions on superficial and preci- pitate remarks, too often forget the nature of an animal, in their anxiety to give it a name. Nomenclature, so useful when ap- propriately employed, ought to rest on a general combination of the structure and H4 PLANARIA ARETHUSA. habits of living creatures, not on isolated features only. Five of the planariz arethusze being stip- plied with fish containing a quantity of clotted blood, in a short time evidently ap- peared to have fed voraciously. The lar- gest, instead of a thin, flat, meagre figure, resulting from scanty aliment, now exhibit- ed a semicylindrical shape, and was con- verted from the predominant leaden tinge to a dull brown colour. Transverse streaks of black or deep grey, constituting the darkening shade of the animal, became very conspicuous by the enlargement of the bo- dy, which had apparently augmented in length as well as in breadth. Something similar to an elliptical intestine, which I conjectured to be the stomach, was, be- sides, perceptible; and this having also been seen in others, induced me to think that here it was certainly so, more especial- ly as its termination might be in that point designed by naturalists the ventral pore. PLANARIA ARETHUSA. 95 Therefore I sought the upper orifice or mouth, but in vain. It cannot fail to excite the surprise of in- telligent observers, that any difficulty should attend a matter of such incontrovertible sim- plicity as seeking the position of the mouth of an animal, of that organ which must be constantly in action for the very preservation of life; in one also where minuteness is no obstacle to discovery: But, so great is the diversity between most of those familiar to our notice, and others more rarely the sub- ject of contemplation, that the arrange- ments of nature seem purposely calculated to bewilder our acutest judgment. All planarize immediately become sensi- ble of the vicinity of food, though whether by means of vision, may be disputed. Their motions then displayed, certainly have ra- ther an opposite tendency ; and hence the likelihood of an olfactory power resident in them, such as may be peculiar to other ani- mals not receiving the immediate rays of light. Nearly a month subsequent to the 96 PLANARIA ARETHUSA. preceding observation, several planariz of the species at present described, were sup- plied with the soft part of an oyster; a sub- stance which they generally receive in pre- ference to the fleshy parts of animals. Some lighter particles floated at the surface, and I saw, with infinite surprise, a planaria also swimming supine in their vicinity, quickly protrude a long, milk-white, tubular probos- cis, by which they were greedily absorbed. No wonder, indeed, that my search after any analogous organ had been fruitless. Unlike that of all other animals with which it is allied, or which come within the sphere of my knowledge, its aperture, instead of belonging to the head, is in immediate approximation to the tail. Situated in the under surface, and towards the lower extre- mity, it proves to be what naturalists have so erroneously denominated the ventral pore. Although this may be deemed a trivial fact in the grand scale of observa- tion, it impressively warns us to distrust analogical reasoning for which we are ena- PLANARIA ARETHUSA. 97 bled to substitute experiment. Of such infinity are the ways adopted by nature for the perpetuation, welfare, and conservation of-her creatures, that analogies in their or- ganization appear unnecessary for the sub- sistence of life. The rest of the planariz then, aware of the presence of food, in like manner began to issue forth their long slender trunks, and either insinuate them into the larger portions of fish lying at the bottom of the water, or absorb the particles suspended upon it. In imitation of the name bestowed on the trunk of the elephant, the extensile organ serving to imbibe the nutriment of many of the smaller animals, is called a proboscis, whether it simply unfolds from the root, protrudes from a sheath, or unwinds from a regular series of volutions. But in none is the designation equally strict and appro- priate as in the planaria. There it is absolutely the organ of the elephant in miniature, with this exception that it is neither annulated, nor composed of seg- H 58 PLANARIA ARETHUSA. ments. It is of surprising length, being little, if any, shorter when fully extended than the whole animal. Its contractility is in proportion, which renders it susceptible of diminution into its respective share, when a voluntary reduction of its owner’s size ensues. If employed, it is either simply cylindrical, flattened, or trumpet-shaped at the extremity, as the planaria inclines; and when stretched to the uttermost, the root becomes an apex of the slenderest cone. It seems of greater consistency, harder, and tougher than the rest of the body, so as to admit insertion into decaying vegetables ; but it is still of a gelatinous, and not of a cartilaginous substance. Accordingly, the Jeaves of plants, before becoming quite soft and mucilaginous, may be seen studded with punctures over the surface, proceed- ing, as is probable, from the operation of the proboscis. If this organ neither consists of rings nor segments, and at the same time alternate- ly lies in concealment within the body, and PLANARIA ARETHUSA. 99 is protruded far without it, a question will arise, how is so remarkable a change ac- complished? In a state of rest, the pro- boscis occupies the place denoted by an el- liptical spot externally visible; and then it is a short hollow cylinder, of greater dia- meter at the mouth. Its extreme dilatibi- lity is effected by reducing the sides of the tube in extension, which reduction is_per- haps chiefly manifested towards the ex- tremity, where the substance is more accu- mulated ; and we must observe, that while, from facility of expression, it is called a hollow cylinder, the whole interior circum- ference is probably in contact. This is a wise provision of nature. The structure of the proboscis intimately corresponds with the general structure of the body; it is susceptible of the same expansion and con- traction; and the incessant change of shape in the one is attended by a similar altera- tion in the other. If, by a dexterous opera- tion, the extended organ be severed from the animal while feeding, an experiment 100 PLANARIA ARETHUSA. which it cannot be desirable to repeat, the aliment continues to be absorbed for a very considerable time, and is discharged from the mutilated end. Regular contractions and dilations are all the time performed as if the proboscis were untouched. On dis- section, the upper part seems to communi- cate with other vessels, traversing the body or branching to each side; but the gelati- nous consistence of the animal, and its in- variable contraction when dead, unite in opposing the researches of the physiologist. Probably this is the only part of a planaria which is not reproduced into a new animal, though it be regenerated where defective. The proboscis of the whole individuals which I have examined, is of a milk-white colour from the root to the mouth. It is entertaining to observe the operation of its functions. The power of the planaria over it seems almost unlimited, and by its sin- gular flexibility, it can be extended, bent, and contorted in every possible directicn. Sometimes it is protruded from the tail t« PLANARIA ARETHUSA. 10] meet the head; sometimes it curves over the back; and in those mutilated by spon- taneous division, it may be seen issuing far behind, in a direction diametrically opposite to the ordinary site of the mouth of ani- mals. On supplying a portion of flesh, the trunk is immediately buried among its fi- bres; or if the planaria can find a worm suf- ficiently small, it is slowly and gradually ab- sorbed, the proboscis ensheathing it by a cy- jinder half as long as the body. Should a number fix on the same object, their trunks, all in action, and greatly extended, are often curicusly intertwined; for each is stretched out by the planaria on becoming sensible of the presence of food, while it remains sta- tionary itself at a considerable distance. It is exceedingly interesting, also, to witness the immediate dissemination of soft alimen- tary substances absorbed by the proboscis, bringing the delicate interanea into view, and changing the hue of the animal; nor is it less singular to contrast the milky whiteness of the organ with the body of 102 PLANARIA ARETHUSA. some which is black as jet. The mouth of the proboscis appears at c in Fig. 15. of the planaria nigra, viewed by a magnifier. The perplexities occasioned from dis- coloration, were illustrated by various ex- amples, which shew the difficulty of guard- ing against error. On the twenty-eighth of January 1813, I took a number of plana- riz indiscriminately from the spring at the Well-house Tower. None of the arethu- see could be detected among them; but several bearing an exact resemblance ex- cept in colour. All the latter were brown of different shades; the head, margin, and site of the proboscis clear; and in some, pinnate ramifications, filled with a bright red substance, appeared. The exemption of the head, margin, and proboscis, from the colour, led me to conjecture that it was accidental, for no perceptible vessels tra- verse these parts ; but in every respect the deception was complete. On the fifth of February, so great an alteration had ensued as to verify my anticipations; yet it was PLANARIA ARETHUSA.- 103 not until the thirteenth of that month, that the doubtful animals were restored to their original grey. Though the proboscis be naturally single, I once saw three in a monstrous planaria of another species than what is treated of in this section, which were all actively em- ployed at the same moment. Apparently no portion of it is lost by spontaneous divi- sion of the body; but how a new aperture is made for its protrusion in a regenerating fragment, I am ignorant. After taking the uses and properties of this organ into view, we must henceforth denominate that the orifice of the mouth, which has hitherto been designed by natu- ralists a conspicuous ventral pore in plana- rie. The mode of propagation peculiar to the Planaria arethusa, is no less involved in mystery, than the perpetuation of kindred species, whose eggs and foetuses have been sought in vain. Notwithstanding | have carefully kept the same individuals for 2 104 FLANARIA ARETHUSA. period exceeding a year, and though I have removed many from their natural abode at all different seasons, I never could be sen- sible of finding either eggs or living young. Not long ago, however, I concluded that the fact was at last ascertained. In a ves- sel containing these planarize, and little else than pure water, several rows of small bright yellow eggs were observed, each row being in a straight line, and consisting of about twenty-four. The like was found, un- der similar circumstances, in another vessel; and I anxiously watched the exclusion of the expected young, for the eggs were in no respect dissimilar from what might have been produced by planarize, except in size: and besides there not being any general rule in this particular, their smallness was a satisfactory reason why they had been detected with so much difficulty. But soon after, the same was exhibited in a third vessel, certainly containing no_planarie, which immediately betrayed the fallacy ; and on more minute investigation, the eggs PLANARIA ARETHUSA. 105 proved to have come from a species of the entomostraca, a small shelled animal, which, according to my calculation, should not have laid an egg one-third as large, and whose presence in the water had been over- looked. Thus if these planariz propagate by eggs, they are still undiscovered. Yet here also the wisdom of* Nature has not failed in providing for the preservation of the race ;—spontaneous division ensues, whereby, as before, a fragment detaching itself from the body of the parent, becomes a perfect animal, while the mutilated por- tion of the trunk is repaired. The diversity of colour in the same pla- nariz first excited my conjectures, that re- production after spontaneous separation had taken place. Six animals were therefore selected for farther observation, four of large, and two of small size. The second day subsequent, which was the fifth of No- vember 1810, I remarked that one of the larger had lost a fragment from the tail, not exceeding a sixth part of the length of the 106 PLANARIA ARETHUSA. whole planaria. In six days, its motion was manifest, and on the eighteenth ofthemonth, a white papillawas vegetating from the sum- mit. The organic reproduction appeared complete on the twenty-second; the new animal traversed the surrounding element, though its figure neither was so well defi- ned, nor were its motions so lively as dis- played by two regenerating fragments of the planaria felina which had separated la- ter. On the twelfth of November, it had nearly acquired the shape of a full grown planaria; and the two specks or eyes were conspicuous with the microscope on the twenty-third. Perhaps they might have been found earlier, had my attention been so directed. The fragments thus separating and_ be- coming perfect animals, never attained the dimensions of the parent whole. While in possession of the observer, they always re- main infinitely smaller. It should also be remarked, that no feeding will preserve the size of any planarize when removed from PLANARIA ARETHUSA. 107 their native abode; for they gradually, though slowly, decline and waste away. Perhaps this may partly be ascribed to the inconsiderable quantity of water devoted to their use, compared with what they enjoy in their natural state; thence rendering them more liable to be affected by external causes; or it may arise from an exhaustion of those principles adapted for the preser- vation of life. The want of mud and other substances into which they might retreat from the impressions of the light and air, may also operate their destruction ; but its chief source centers in some noxious prin- ciple contracted by water. If remaining a considerable time unchanged, the planariz decrease more rapidly, they become lan- euid, scarcely moving either by the influ- ence of light or heat, and at last adhere entirely to the side of the containing ves- sel, where they perish. Relative to this subject, I remember that when engaged in experiments on these animals in the city of Edinburgh, though thriving well, and 108 PLANARIA ARETHUSA. feeding readily when supplied with the wa- ter on the south of the town, they lan- guished and died when transferred to the opposite quarter. There the water com- monly used by the inhabitants proved insa- lubrious. The naturalist should therefore always search for what is already inhabited by animated beings visible to the naked eye, before consigning those to it in whose preservation he is interested. The subsequent alteration of proportion in the different parts of a fragment sepa- rating in the species arethusa, is not dissi- milar from what is witnessed in the pro- gress of the felina. Between the eleventh and seventeenth of January, a portion de- tached itself from the extremity of another of the six animals selected for observation. On the tenth of February, its figure and proportions approached to those of a plana- ria in miniature ; the original breadth was greatly diminished ; the head, instead of being a shapeless projection, was connected to the body by a well-formed neck; and the PLANARIA ARETHUSA. 109 general contour was distinguished by a re- gularity which belongs to perfection only. On the thirty-first of March, a considerable enlargement had succeeded, and the young planaria possessed all the properties and characteristics of full grown animals. At this period, also, the tail of the parent was completely renewed, but the substituted part marked by a certain péllucidity inva- riably indicative of reproduction. Both the original animal, and the offspring which constituted the separating fragment, are represented from life, Fig. 11. 14. Propagation in this way is a much more rare occurrence, than with the preceding species, in which it is described. A num- ber of the feline being indiscriminately taken from still water, on the twentieth of July, some proved of the largest size, others minute, and several had undergone spontaneous division; they either want- ed the lower extremity, or portions de- tached were in progress of acquiring the defective organs. The following day, I 110 PLANARIA ARETHUSA. fished up a number of the arethuse now under discussion, from a spring well about half a mile distant. All were entire; no separated fragments appeared; nor had I for long observed any divisions among those kept in my apartment. On the whole, it rather seems to me, that the circumstance of removal from the place of their natural origin, renders these animals more subject to spontaneous division of the body ; and in general it succeeds soon af- terwards. There are exceptions, it is true, which are not easily susceptible of explanation; and conjecture alone can ascribe them to age, sex if there is sex, or the distinction of it in the arethusze, or to their preservation from any kind of constraint or suffering. Those of certain waters are, besides, apparently less liable to it than the planariz of others, which may infer a difference in the species diffi- cult to be recognised by observers. But with the planarize felinze such partition is incessant in every different size, and in all PLANARIA ARETHUSA. lll seasons, conditions, and situations. Scarce has it happened once, when it seems ready to happen again, and still with impunity to the remainder of the animal. Hence the increase of this species advances with in- comparably greater rapidity than that of the other. Although it has not been my fortune to find the eggs either of the felina or arethu- sa, those which have chiefly been subjected to observation, I must repeat, that it is not here affirmed there are none. The difficulties opposing the solution of prob- lems far more simple than the secret ope- rations of nature, are a sufficient warning against gratuitous assumptions. Yet in contrasting the various species among themselves, it is certainly very singular that I have never witnessed spontaneous division among those which produced eggs in my possession, or which were disco- vered in the waters. Should this distinc- tion be proved absolute by future observa- tion, it forms an additional phenomenon idg PLANARIA ARETHUSA. in the history of the genus, no less remark- able than those distinguishing the indivi- dual species that compose it. Still, it is a conclusion which we should beware of adopt- ing, without the test of rigorous experi- ment. {éi08 The powerful reproductive principle re- sident in the various parts of the arethusa is seen in its multiplication, from artificial sections. All are speedily regenerated in- to entire animals, their progress and _per- fection being dependent on the usual laws which regulate the evolution of defective parts. Monstrosities are sometimes found, of which an example has been already quo- ted; and at another time, one was taken with two complete tails of considerable length, neither of them resembling an ac- cidental production; so that it was doubt- ful which was original, or if either had pre- ceded its fellow. Bifurcation of the tail is the most common kind of monstrosity in the genus, but it is probably to be in gene- ral ascribed to accident ; and we can more PLANARIA ARETHUSA, 113 easily comprehend why it may be so, than we can hazard an explanation of its ascend- ing to original conformation. This species of planaria is not so often seen in a state of repletion as the rest; nor does it dwell indiscriminately among them. I have on no occasion observed it in stagnant water; whether from being less congenial to it, or because its ordi- nary food belongs to springs, I shall not presume to determine. Certain bounda- ries are assigned by nature to all her crea- tures: the largest quadrupeds and the mi- nutest insect are alike restrained within the respective barriers of place and climate, which may not be safely left behind. The elk cannot dwell with the elephant; the foot of the camel is formed for the parched and sandy desért; while that of the goat is fitted for climbing alpine mountains. The flight of the tropic bird is confined within the li- mits from which it derives its name; and many inhabitants of the vast Pacific Ocean are banished from the northern seas. The I i1l4 PLANARIA ARETHUSAs numbers of the scorpion, and the deleteri- ous activity of its poison, decrease as it re- moves from under the line ; and the necta- rious collections of the bee ate adapted to those regions only which admit the bloom of flowers. Let us traverse the shores of our native islands; within a determinate boundary, we shall find a particular tribe numerously disseminated, and in vigorous life; proceeding a little onwards, fewer ap- pear in their. haunts ; and advancing still farther, the race totally vanishes.— Lhen another is seen, which, from at first being scantily associated, becomes at length the sole tenant of the territory. Diviston Ul. Planaria Gramimea, Fig. 16. _-Jt must not be conceived, that all the animals hitherto ranked under the genus planaria by naturalists, bear a common re- semblance, either in organization or pro- pensities. So wide a difference in both ap- pears among them, that one intermediate tribe, somewhat more approximate to the PLANARIA GRAMINEA. 115 leech, might perhaps be constituted, and others analogous to worms. Trivial dis- tinctions, indeed, should be disregarded, not only to avoid the multiplication of ge- nera, which would thus be extended to in- finity, but to simplify the arrangements of Natural History, and render them compre- hensible from prominent features. Yet to include in the same class creatures provi- ded with organs totally wanting in those associated with them, subsisting on food of opposite qualities, and living in different elements, which would reciprocally be fatal to their existence, certainly does seem an anachronism, and is not easily reconcileable to strict and logical reasoning. The precise place which the animal that shall be here denominated planaria grami- nea should occupy in the system of nature, has been controverted by observers. Some have called it a planaria, others a leech, and in truth it perhaps participates of the general characteristics of both. Therefore, to shun the perplexity which the multipli- “ 116 PLANARIA GRAMINEA. cation of genera creates, it is now retained as constituting a second division of the ge- nus planaria. The distinction is principal- ly founded on the shape of the animal, the position of the mouth, and number of eyes. The planaria graminea is of a beautiful grass green colour, and by the aid of a magnifier, perceptibly speckled with black; but to the naked eye, the surface of the skin is uniformly green. Its figure is a double cone, truncated at one extremity the head; and the termination of the tail is the opposite apex. Thus the planaria is not flat, and the head is obtuse. Near to the termination of the truncated part are two very black specks or eyes, far asunder, one being on each side of the head. I have not been able positively to ascertain whether there are none other of smaller size; for it is not impossible that, under favourable circum- stances, the most powerful magnifiers might bring such into view. In the leech, at least, with respect to certain species, particular difficulty sometimes attends the discovery : eee PLANARIA GRAMINEA. 117 of the smaller eyes, and naturalists ought not hastily to conclude that those exposed at the first glance, or even by a moderate magnifier, are all which that singular ani- mal possesses. The voluntary contraction that every portion is highly susceptible of, and the casual obscuration of parts by in- tervening shades, tend to withdraw the mi- nuter organs from observation. If the two black specks of the planaria graminea be designed for the purposes of vision, as their position and appearance would indicate, their operation is assuredly of a different kind from that of the eyes of terrestrial ani- mals. Sometimes these planariz# rush against obstacles which they are apparent- ly desirous of avoiding ; nor when two are close together, do they always seem sensi- ble of their mutual presence, and on acci- dental contact, they suddenly contract, and reciprocally retreat in alarm. The whole bo- dy, which is scarce two lines in length, and half as thick, in the middle, where perfect- ly round, is invested with a thin transpa- 118 PLANARIA GRAMINEA. rent integument, especially conspicuous at the head and tail. Compared with the motion of the larger planariz, that of the graminea is surprising- ly swift, to which its peculiar figure, in ren- dering it more buoyant, contributes. But unlike the others, its adhesion to surrounding substances is slight ; and when replete with food, its ascent on the side of a glass vessel is accomplished with difficulty. The tail, though quite taper and acute, is principally ~ employed for adhesion ; however, it has no resemblance to the corresponding extremi- ty of the leech, notwithstanding there is some general analogy of motion, contrac- tion, and dilatation, between the two ani- mals. Trusting to the classification of the gra- minea by nomenclators, along with the species of planarize most familiar to me, I supplied it with various kinds of food, ex- pecting the speedy protrusion of a retrac- tile proboscis. None, however, appeared ; nor was it possible, on the strictest scruti- FLANARIA GRAMINEA. 119 ny, both with the naked eye and magni- fiers, to discover the wonted aperture of the mouth in the surface of the belly. The position of such an aperture, known under the name of a ventral pore, is, as before re- marked, a principal feature in the organiza- tion of planarie. ‘There were few vegeta- bles in the water containing those of which I speak, nor any approaches to maceration, neither did it include the decaying remains of animal substances; and meanwhile the planarize, contrary to the nature of all that had been previously examined, continued equally plump and large as when originally taken. From this it was probable that they did not subsist on vegetable aliment ; and their constant action as if in pursuit of prey, inferred that it might consist of aquatic ani- malcula. The head in their courses, was frequently directed against those that lay in the way. They long rejected every dif- ferent substance presented, until supplied with the soft parts of oyster, which had pro- ved so grateful to the rest. Then, when in 120 PLANARIA GRAMINEA. a favourable situation, instead of a proboscis issuing from the belly, a wide mouth was seen to open towards the anterior extremi- ty, which greedily swallowed the food, and the animals acquired a sensible augmenta- tion of size. Unless from the usual green being of the faintest dusky shade, the po- sition of the mouth, when close, is scarce, if at all to be recognized. Therefore, should the learned Muller by ora candida, refer to this organ, his planaria helluo is different from the graminea; nor, indeed, is there the smallest speck of white on any part of the whole animal. In the latter, the mouth lies under the most prominent part of the head, which may aptly be deno- minated a snout. ‘The planaria snaps at its prey like a fish, and if unsuccessful, crouches away under evident discomfiture, to await a better opportunity. It does not hesitate thus to attack animals twenty times its own size, and is continually attempting to swallow those infinitely too large for deglu- tition. The site and figure of the mouth PLANARIA GRAMINEA. 121 of the graminea, therefore, remove it from the same division of the genus comprehend- ing those provided with a proboscis; and there is still another line of distinction, in the visible corrugations or inequalities sometimes exhibited by the body, whereas the others are perfectly smooth. Like them, it swims supine at the surface of the water. These planariz are hermaphrodites, in the strictest sense ; but whether impregna- tion originally results from the sexual union, may be called in question, not perhaps as to the vivifying principle, but with respect to the formation of the egg. Some years ago, the animal was not un- common; and in the course of casual in- spection, I had frequently remarked an egg within the body; in as far as recollection serves, the species was the same. Its su- pervening rarity, however, of later years, partly arising from the progress of agricul- ture, so inimical to the pursuits of the na- 122 PLANARIA GRAMINEA. turalist, impeded further researches in the vicinity of my usual country abode. Two being taken on the twenty-fourth of September, were carefully preserved in a glass vessel, and for some time regularly supplied with water from the place whence they had been removed. Both were of a beautiful uniform grass green colour, at- tended by a pellucidity at the extremities denoting the investing integument. In six days, the interior began to darken; and in seven more, four dusky ovuli were per- ceptible within the larger of the planariz, for the two animals were of unequal size. On the eleventh of October, they had in- creased to the number of six, and some were also at that time visible in the smaller animal. They were differently disposed, however, in their respective ova- ries; all belonging to the latter being ran- ged on one side of the lower extremity, while those of the former were distributed in both. PLANARIA GRAMINEA. 128 Soon after, the sexual union took place, during which the two animals, adhering by their tails to the upper part of the glass, performed a singular conjoint revolution, resembling the spokes of a wheel. Similar gyrations are occasionally exhibited by them singly in the water. The eggs, now visi- ble by the naked eye, appeared in various stages of maturity, and in greater number; they were still ranged on one side of the smaller planaria, and some which had re- cently been near the opposite extremity, rose so high as to approach within a third of the snout. Subsequent remarks established, that the animal, in assuming different positions, can bring other eggs than those at first most conspicuous into view; and it even seems endowed with the faculty of altering their place in its body. Instead of the regular arrangement preserved in an early stage, they gradually became more confused, se- parating, as it were, into detached groups and clusters; and on the eighteenth of Oc- 124 PLANARIA GRAMINEA. tober, one in the larger planaria, had rose towards the site of the mouth. A few days afterwards, this latter cir- cumstance attracted farther notice; for in the smaller animal, two eggs were so close to its mouth on the twenty-fifth, that I an- ticipated their production from some ovi- duct in its immediate vicinity; and next day one of them was almost between its eyes. Description can convey but an im- perfect picture of these successive changes; nor can their singular appearance, their force, and effect, be adequately conceived by naturalists unacquainted with the sub- jects of observation. But such an altera- tion of position was the less to be account- ed for, from not being the result of too re- stricted space in the body. of the planaria. Various interstices separated the eggs them- selves, or their clusters from each other, whereby the animals seemed speckled to the naked eye. When the truth was just about to be realised, the smaller one unfortunately pe- PLANARIA GRAMINEA. 125 rished on the twenty-eighth of October, and the larger on the thirtieth, without any sensible cause for the death of either. We know that there are certain animals whose life draws to a conclusion on the at- tainment of maturity; and there are some which die in giving birth to their young. Many, among the insect tribes, which have passed a protracted interval in successive stages, have but a transient enjoyment of existence in the perfect state. ‘The butter- fly, whose gaudy colours announce the ap- proach of summer, seldom witnesses its ° termination. When the immutable laws for the conservation of the species are ful- filled, the males of the honey-bee are des- tined to perish by violence, at an appoint- ed season; and the ephemera of the morn- ing scarce survives the close of day. Nay more; the volvox globator, a beautiful green spherical animal, includes several successive generations at once within its body. All the vital functions are performed ; it origi- nates, grows, and reaches perfection. Then » 126 PLANARIA GRAMINEA. it bursts to allow an exit to its young; and the investing integument, scattered in the surrounding element, disappears. Such is the unalterable condition of its own exist- ence. But this is only a single race. The offspring, now independent, swim through their native fluid, each revolving on its centre as an axis, the whole under- go the same gradations, and each is desti- ned to be extirpated by the same fate which destroyed its parent. By the death and subsequent decay of the planaria graminea, eighteen eggs esca- ped from its body. I do not affirm, how- ever, that, like the volvox, the life of its offspring is decreed to result from its own destruction; for circumstances have pre- vented researches which might corroborate the fact. No visible cause of death, in- deed, was shown: Yet if life in the larger animals hangs by so slender and delicate a thread, that its perpetual rupture insensi- bly ensues, even when danger is anxiously warded away, how infinitely greater is the PLANARIA GRAMINEA. 127 liability of those diminutive inhabitants of the waters to perish! Not only is the war- fare eternally waged by the stronger, fatal to the weaker without resource ; but some deleterious principle suddenly imparted to their native element, may sweep them off in legions, or prove their absolute eradica- tion. Judging by the apparent maturity of the egos, I entertained hopes that part of them might have been hatched, and thus furnish a new colony for observation. Possibly this would have followed, had all that care and attention been bestowed upon them, which objects so minute require. However, though long retaining their original hue and ap- pearance, none produced young. Planaria Velox, Fig. 17.—It has been said, that the vegetable creation is more diversified and luxuriant on some solitary hill, amidst wide-extended plains ; and so it has seemed to me with respect to animal life in marshes far asunder in a fertile re- 128 : PLANARIA VELOX. gion. fs it because such an infinity of the insects with which the universe teems must first have an aquatic abode, preparatory to the perfection of all their organs? or be- cause the abundance of decaying matter, whose maceration is promoted by humidity, affords an uninterrupted nutritious supply ? or, finally, because the receptacles being fewer, the aggregate is greater in propor- tion ? Towards the latter end of September 1812, several capacious vessels were filled with water from a marsh situated in the centre of a cultivated district. As the con- tents subsided, uncommon variety of ani- nals appeared. Numerous aquatic insects complete, or larvee advancing to their suc- cessive metamorphoses, performed their agile evolutions, or sluggishly dragged their members along. Beautiful hydrachnee, decked in velvet colours, were ardently oc- cupied in the pursuit of prey; many de- fenceless beings sought shelter amidst the weeds and slime; and myriads of minute PLANARIA VELOX. 129 anguillze suspended in the fluid, fell like a flocculent substance, to whiten the dusky deposit below. While viewing the incalculable millions here concentrated together, I observed some diminutive animals quickly ascending the sides of a vessel, which on gaining the boundaries of the element, committed them- selves to its surface in swimming supine. Being separated from the rest, they proved, on more intimate investigation, to belong to that tribe with which we have been so long engaged, and possessed of properties denoting their alliance with the species last described. The planaria velox exactly resembles a weaver’s shuttle, and were it not from cer- tain peculiarities specified by Muller, it might be considered the same which he has designated rostrata. Whether these pecu- liarities are temporary or permanent, has not been explained; sometimes the simple difference of the season of inspection may persuade us, though erroneously, to insti- K 130 PLANARIA VELOX. tute an additional species, as if different from those already known. From the an- terior part of the body, the head is protract- ed into a long pointed snout; and the tail, almost equally long and slender, terminates in an angle proportionally acute. On the upper surface, at a considerable distance behind the head, are two blood-red eyes, which may almost be said to sparkle in the sunshine. The body seems of a fleshy consistence, more so than that of the others, and it is invested by a transparent integu- ment, through which the interanea are con- spicuously exposed. A dull white colour pervades the whole exterior; and the en- tire length of the animal is about two lines, or a sixth part of an inch. In searching for the mouth of this spe- cies, a part of its organization, which will tend to establish its real place in the ar- rangements of nature, I have hitherto been unsuccessful. But most probably its site is analogous to that of the former, and PLANARIA VELOX. 131 somewhere under the projection of the snout. It is a lively, active animal, swiftly tra- versing the surrounding substances, with its snout incessantly in motion as if in quest of prey; and as its size is not speedi- ly reduced by confinement, it possibly sub- sists on aquatic animalcula. The planaria velox is distinguished by _ remarkable timidity; its adhesive. facul- ty is so slight, that the containing vessel can scarce be touched without the conse- quent cessation of its hold. . The same, in- deed, is a leading characteristic of all other planariz, though in a far inferior degree; they suddenly abandon the plane of posi- tion, and drop through the water, with con- tortions of the body, as if to break their fall, while they are evidently aided by a fi- lament invisible to the naked eye. This planaria propagates by eggs, which are arranged in an ovarium of two rows, one as if belonging to each side of the bo- dy. Their number is exceedingly various, 132 PLANARIA VELOX. consisting, in the different animals, of from one to sixteen; but their origin and progress were not observed, and as all are not pro- duced at once, I cannot affirm how many are peculiar to the species. A planaria se- parated from others on the second of Octo- ber, had next day laid twelve eggs, while one remained in the body some time longer. These eggs are of a dark brown colour, and perfectly spherical ; those of the former species are of a long ovoid, and of a clear, transparent, reddish brown : they are attached in a cluster either to the sides of the vessel, or to any floating substance in the vicinity. Probably weeks are required for their exclusion. Such seemed the result of observations made in November, when I found the shell broke, and the young that had escaped. Minute crimson specks were perceptible in one of the parent planariz, and having previously remarked the same appearance in several individuals, I was induced to con- sider them the incipient evolution of an ova- PLANARIA VELOX. 133 rium which another season would bring to maturity. Prosecution of this enquiry was inter- rupted, from the total evaporation of the marsh where the animals had been found, by an uncommon drought during summer 1813. Thus the race may be extirpated there, unless, which is not improbable, the revival of humidity shall promote the ex- clusion of eggs accidentally preserved, and which have not lost the latent principle of vitality. Planaria Edinensis, Fig. 18.—The differ- ent genera of animals are constituted by uniting individuals bearing the greatest re- ciprocal analogies in habits or conformation under some common characteristic. But a subordinate distribution into species soon becomes necessary, from more attentive examination discovering peculiarities in one which are wanting in another. The plana- rie of the former division are united by structure, in a proboscis protruding from 134 PLANARIA EDINENSIS. the belly, and by general correspondence in figure and motion: the species are dis- tinguished by the variety, number, and po- sition of eyes, the presence of: tentacula, and mode of propagation. - A second divi- sion arises from the appearance of the ani- mals, conjoined with the site of the eyes and mouth, in which a prominent charac- teristic is the want of a proboscis, so far as can be ascertained. Though nearly the same leading features belong to the subject of this section, perhaps it might more .cor- rectly have preceded the two already de- scribed, or stood as an intermediate race. The planaria Edinensis, so called from inhabiting the discharge from the Well- house Tower, near the castle of Edinburgh, is about a quarter of an inch in length, and slightly tapers upwards from the lower ex- tremity, which terminates abruptly in a point; while the head is obtuse, and void of tentacula. In an ordinary state, the body is flat below, convex above, and with a longitudinal ridge, apparently elevated, PLANARIA EDINENSIS. 135 down part of the back; but after feeding copiously, the whole, from distension, as- sumes a conical form, and the pointed tail is obliterated. The body is smooth and shining; its general hue is the palest car- nation, the anterior is rose colour, and the ridge in some tends to cream colour or dull white. Two black eyes are seated near the front, in the rose-coloured part, which in young planariz are ovoids, but in grown animals considerably magnified, appear 1r- regularly globular. In the under surface, a little behind the corresponding position of the eyes, there is a long slit situated in the centre of an indistinct ellipse clearer than the rest of the body, which seems to contain the mouth, and perhaps also the termination of an oviduct or excretory ca- nal. This planaria, like the others, is carnivo- rous: it feeds voraciously on flesh, after which it is so greedy as to leave the water when in the immediate vicinity. On such occasions, it has received no injury; and » 136 PLANARIA EDINENSIS. the planarize of the division to which it per- tains, seem to support slight and transient desiccation with greater impunity than the rest. The body is much enlarged, and dis- tended into an utricular shape by feeding : it seems hollow within, and the interanea are apparently lodged in the circumference. Globules of air are frequently absorbed along with the food, which reduce the ani- mal’s specific gravity so much as to render it incapable of descending in its fluid. It sucks its food like the leech, which, contra- ry to the general opinion, is an animal highly carnivorous ; and the examples daily given of its surviving incredibly long in pure water, instead of being admitted as demonstration that food is unnecessary, ought rather to be ranked with other pro- digies of living beings enduring abstinence. Marsh water, frequently renewed, will al- ways prove a salutary supply. The planaria Edinensis propagates by eggs, which are invariably seen in the same situation near the orifice of the mouth, PLANARIA EDINENSIS. 137 though only one be visible at a time. A planaria which had retreated among the mud during the winter months, appeared on the side of its vessel on the thirteenth of February, bearing a single egg of light chocolate colour, extremely conspicuous through the thin integument below. In three days it had been laid, and its place was vacant; but on the twentieth of the month, another egg was seen in the site of the former, or within a third of the anterior extremity. I then removed the animal in- to a watch-glass, where it might always be accessible, in expectation of obtaining the egg, and found it accordingly at the bot- tom, on the following day. There was now no appearance of any more in the parent ; and on the twenty-third, a very minute planaria of the same species, as nearly as could be determined, was vivaciously tra- versing the liquid. In the evening, how- ever, the planaria exhibited a third egg, si- tuated exactly as the two preceding, of which also it had next morning divested 138 PLANARIA EDINENSIS. itself. The sudden appearance of an. egg always in the same stage, without my being able to observe its progress, and seldom be- ing capable of discovering it when deposited, induced me to suspect that it might possi- bly be taken up into some pouch or cavity by the neighbouring aperture. But this pro- ved an erroneous conjecture; for the eggs, amounting to six or more, are successively produced at certain intervals ; and notwith- standing their sudden attainment of matu- rity, and one only being visible at a time, they are sometimes to be observed previous to coloration, of an opaque white. Proba- bly they successively ascend towards the head, in conformity with those of the pla- naria graminea, rising from an ovarium somewhere in the side. The egg is void of any viscosity, unlike that of the black planaria, which I have seen floating at the surface of the water, imbedded in a lump of transparent jelly: it has a hard shell, and is perfectly globular. Most minute objects, however beautiful and PLANARIA EDINENSIS. 139 symmetrical to the naked eye, are rude and deformed under the microscope; but it is otherwise with the egg of the planaria Edinensis, which still remains a regular and equal sphere when viewed with the highest magnifiers. One young animal is excluded in twenty- eight days from each egg, at first milk- white, and endowed with uncommon viva-. city. The reproductive powers of this planaria have much less energy than those in the species above described of the other divi- sion. Artificial sections are long of acqui- ring the defective parts ; and when they do vegetate, they are not so well defined. Du- ring a mild season, neither the head nor the eyes were evidently in progress to re- production during fourteen days. This animal is of a shy and timid disposi- tion; for months it dwells constantly in the mud, nothing except the snout being protru- ded above it. If venturing to traverse the surface, it hastily retreats to concealment on 140 PLANARIA EDINENSIS. the slightest motion or alarm ; and with me it remained completely buried from Octo- ber until the subsequent February or March. Planariz are totally defenceless ; their progression is ill adapted for withdraw- ing them from sudden danger ; their bodies yield even under gentle pressure; their senses are not eminently acute, nor is their instinct active ;—thus they seem incapable of resisting an enemy. We are wont to assume, that nature has formed no animal without-providing it with the means of pro- tection; but it cannot be denied, that al- though many are endowed with fleetness on the earth, or flight in the air, and that some are possessed of tusks, or horns, or a deadly sting, greater solicitude appears tes- tified for conservation of the species, than for the security of individuals. The pla- naria Edinensis may find shelter from its enemies in mud, or its sustenance may be derived from what is usually precipitated along with it. CONCLUSION. 141 Amone the general conclusions which may be deduced from the preceding obser- vations, it appears that the genus is suscep- tible of subordinate divisions, according to peculiar organization; though analogous properties are seen where the structure is different. In one extensive class, the aper- ture of the mouth is remote from the head, and under certain circumstances, is even diametrically opposite to it. This aper- ture is the extremity of an exsertile tube, by which the food is conveyed into nume- rous viscera, distributing it by delicate ra- mifications throughout the body. Should the substances which are voraciously ab- sorbed, be coloured, the hue of the whole planaria, except the head and a marginal band of the remainder, is altered. By means of an organ probably situated to- wards the tail, a glutinous or silky matter is prepared in threads, which are singly in- visible to the naked eye, but become per- ceptible when accumulated in numbers. 142 CONCLUSION. However, it is not ascertained that such a property is common to every species. Pro- pagation is effected in two distinct. modes, void of any relation or analogy to each other; being either by an egg containing one or more young, or by the spontaneous separation of a fragment of the tail, which becomes a perfect animal. But no disjunc- tion of parts takes place in those spe- cies producing eggs, nor have eggs been discovered where the race is perpetuated by separating fragments. The reproduc- tive principle is enjoyed in the highest per- fection by the genus, whereby not only the most dreadful lacerations are speedily heal- ed, but wanting portions are repaired, and, by a strange anomaly from the laws of or- ganic life, the duplication of essential organs may be artificially obtained. The preceding remarks are far from ex- hausting the history of planarize. Pheno- mena equally singular and interesting are displayed by other species inhabiting the CONCLUSION. 143 sea, or lakes and marshes, though not enu- merated here; and many have yet to be withdrawn from their native abodes, whose nature will further unfold the genuine prin- ciples of animal physiology. EXPLANATION OF THE FIGURES. 1. Tue upper side of the Planaria Flexilis, wherein the specks or eyes may be discerned. 2. The under side, exhibiting a faint indica- tion of the site of some of the viscera. 3. Planaria Nigra, viewed from below. 4. Its egg magnified. 5. One of the young magnified, to shew the position of the marginal specks or eyes. The cylindrical appearance denotes the situation of the proboscis. 6. 7. The upper and under surface of the Pla- naria Panniculata. 8. Planaria Felina, as seen from above. 9. A fragment of the same animal, which has detached itself by spontaneous separation, to be- come a new Planaria, magnified. L 146 EXPLANATION OF THE FIGURES. 10. A Planaria Felina with two heads, the second of which has been artificially produced ; seen from below. 11. 12. The upper and under surface of the Planaria Arethusa. 13. The upper surface of another of these animals, somewhat magnified, to shew the posi- tion of the eyes. The clear line indicates the site of the proboscis; the lower extremity being its aperture on the other side. 14. A complete animal, reproduced from a fragment such as 9. which separated from the tail of 11. 12. 15. The Planaria Nigra, magnified, to shew the site and operation of the proboscis.—c, its mouth: a, the head of the animal; 8, its tail. The Planaria is somewhat more contracted when this organ is so much extended as represented here. 16. Planaria Graminea of the natural size, and as seen by a magnifier. 17. Planaria Velox, of the natural size, and magnified. 18. Planaria Edinensis, magnified. SS ANALYTICAL INDEX. Page CerTAIN aquatic animals enjoy singular prerogatives, . 1 Pham arize, si 36 A NS I RS CES OA 3 Seneral chanacteristies; a0 6 6 eve a ce HORS 4 Apparently akin to the leech and the snail, ...... ib. The genus admits of subdivisions,............ ib. Biararen Flexitlis, cA. eos POR Og 5 RESP SC GES re hat che ih ih clt SV ah Sh aid ah as IRD NS PAE 6 Difficulty of microscopical observations, which should Pac creel Tay chang, ae (3 Se ACPO AG RBIS. SAS “4 The nature of vision is obscure in the Mollusca and Ver- HINO SEY reiy ct sh wk cidclce be te Ponce rep oh tee eae ie MeN suns wey: 8 Planariz in general court the light, ........... 9 The size of the Flexilis is affected by food and tempera- BIBT STS roe say BS ERS cy BENDads Oar now MeL wae Mote We tk bate . 10 TGns Carnivorous. ee Lace tie Que BAOerels 11 The whole body is discoloured by the food, ...... 12 Errors inseparable from superficial observation, .... 13 The grosser parts of food are distributed throughout the FRCS We hss Lockhe Hee RU TE he CS Glam ane ia eeeaies 2 15 This animal is extremely voracious, ........... 16 It perishes from inordinate feeding, ....... sae te Remarks on the Polypus and Actinea, ......... 18 The Planaria Flexilis dwells in society, ......... 19 Mode of obtaining and preserving aquatic animals, . . ib. Propagation ofthe’ Flexilis,)...5.).0005 2 8 2 ee a 20 Artificial sections become perfect animals, ....... 21 pmeinaria NIRA, {Fr Soy a 2 SAS Por AD 22 It is tenacious of life, ....... ofS SAO 26 148 ANALYTICAL INDEX. Page. Experiments proving that it has specks or eyes, . . . . 27 Their position and number, .......--++++++ + 28 Propagation by an egg, ..- +e eee eee ee eee es BY It is imbued with a viscous matter, ........... ib. Several young come from it, ........-.2+-+-- 30 Period required for their exclusion, ..........-. 31 This animal enjoys high reproductive powers, .... - 32 Regeneration of parts depends on the prevailing tem- PETAUAEE) LS Le fee tI Ye eee Ss lost cae ELC RMR a ib. New organs are colourless, ........... ote wae A gluten or mucus exudes from the body, ....... 34 MMonstrosities. 5) 65.0 viele Jeul sy oslaweks SNR is Seen ee 35 Individuals of doubtful species,....... FRR be a ib. Planaria Panniculata, ...... Beth Site he tate RE tcc It is not so common as the Nigra, ............ 39 Propagates by eggs,.....-..--++-:. le ete ee 40 One young Planaria or more comes from each egg, . . ib. Planarie extirpated by diseases, ............. 41 Planaria FPelinas).\).)(o).vsJeije (e's ch ch nae al Seeing Shee It is provided with real tentacula,........... . 43 Number of marginal specks or eyes, ...... ++. 44 Tt: livesvinisocietiys iis) 20) Lenses otis we neice) Sed a ie Remains quiescent next the light, .......... . . 46 Planariz form a glutinous or silken thread,...... . ib. Eood. ofthe Felina) aot. cia aie eh ee Dre Mea, Doubtful if it propagates by eggs or foetuses,. ..... 49 Propagation by spontaneous division of the body, . . . 50 The fragment separating is of uncertain size,...... 51 It is quiescent after separation,.............. 53 Progress and perfection of reproduction, ........ 54 Successive separations of the same body, ........ ib. The organization of the sundered portion is obscure, . 58 Regeneration is affected by temperature, ........ 59 No other mode of propagation has hitherto been ob- served; <.,.. .slstdmn ahiaeetet Le 60 Examples in other animals, .... ...4..2.-22024- 61 Natural monstrosities; ssid). 6 42! se were ieies ce.) HBS ANALYTICAL INDEX. 149 The head of a planaria lost and renewed,....... . 65 ‘Pree: heads'on ene animal,’ .°.'./ 02 2's 2S ead). ib, Experiments to obtain redundant organs, ....... . 67 Spontaneous division and renewal of parts,...... . 69 A supernumerary head may be produced by experiment, ib. Purpose of nature in reproductions, ....... ete TO Sensorium of Planariz,........ ery SE a fees ZAR Two heads are frequently of opposite inclinations, . . . ib. A second head, artificially produced, grows as large as its fellas, a: ix ie aaa sod Aree eae te WARS Us 73 An incision in the side of the Planaria produces a su- pernumerary head,......... JOHNS RE 74 Artificial regeneration is accomplished with greater dif- ficulty than reproduction by natural division, ... . 76 Is there a certain point from which either a head or a tail will be generated?..... SL EUS Tee NOs Man Resemblances to artificial sruriserostiies are sometimes found in the natural state; ....0..... Sra A Sn ea A tendency to action prognosticates the regeneration of * head. ..-22008% 3 MAST ARMS Ee: ot Rurey 80 Wafural nionstrosities, 6000 5 '. 5296 Ce ee 98 The source of monstrosity is obscure, ..... Dietetics, OF Planare: Arethiaay tie 441 Posies aie Bet. Go Errors of naturalists,...... ili sis Cer ieee wb: Animals disappear from their wonted abodes, .... . 87 Description of the Arethusa,........... Ser trae Maricties; 6 i) .9S.6.o0 SPP es cee ae etre eo SG BAYES =. op ula, Sh SD ees Sh ov a. AD SOP ae ees. sO Praboscis,. 200. sn SS RD Gow av Rabe HAN ak 93 Its singular situation,. ..... cyat oped amare tel 36 96 It is of gelatinous consistence, ...... srl AUR Boe Itsiextreme flexibility, yes, 0. ei Mh Oe Observers are liable to deception, ..... of MS PSON cc ie Propagation of the Planaria Arethusa, ..... S07 Bea HGS A fragment separates from the body, ......... 105 Period requisite for regeneration,. .. . . Prac - 106 Complete animals from fragments are smal], ..... ib. 150 ANALYTICAL INDEX. Page. Water contains a certain pabulum beneficial to its in- Miabitants, 9.2. , +. ac sces x ea gOERRESITE allen aire SINISE 107 Progress of reproductions,. .. 6... ++ e+e ee ee 108 Spontaneous division occurs more rarely than in the Planaria Pelina) si ioacad wires eden iag 109 Possibly it is promoted by the suffering of the animal, 110 This Planaria has not been observed in stagnant water, 113 All animals are restricted to certain climates, ..... ib. Trivial distinctions should be disregarded in the clas- sifeation (OL animals, cL H eh dele) Teh sido) Oa siwh olds PlanagiavGaeiasianetns 1) 21 ASLeE a9. Toe choise old woh Manieleite 116 Its motion is comparatively swift, ........... 118 Positianiof the mouth, sic npekieig 4d sundoctarwie den Enid 120 . This Planaria is a hermaphrodite, ........... 121 It propagates by emma; Uesi le aheid We aij. idtoe 6 iS 122 _ Their position in the animal alters, ..... wy are eS The oviduct is perhaps near the mouth, ........ 124 Some animals die in giving birth to their young, . . . 125 Number of eggs in the Planaria Graminea, ...... 126 Myriads of animated beings inhabit marshes, ..... 128 Phinaria: Velo 0) avec Bear: ee TE Nee 129 Kevhas, Ved ‘eyes, io ya) oveeien Ub we tea kncericle te Aaa 130 All planariz characterized by dropping through the DWV eR 7057 oy vay) octronyauiesdisiu's We Vieliiel hn e:j0/ ye Pen DION tie 131 Number of eggs in the Planaria Velox,......... 132 Planaria Edigensis, 200/226, oy eee aes 134 Sitesoh the mouth) |): jo Pee eke ie eee 08 ie ack Baw SSE 135 The shape alters from feeding, .............. 136 Appearance and position of the egg,.......... 15 Tttis void jaf viscosity, i. (os. bo 2 We eae Wee 13 One young Planaria comes from each egg, ...... 139 Wature.of this ‘animals. )..005 sinih evs. ct abeemone eiewene ib. Planariz are defenceless creatures, ........... 140 General conclasions, «thurs atcusin ) Ane Gi ae 141 FINIS. 65) De ERRATA. Page 73. line 11. for left side read right side. __. 74. —- 13. for asevered read a severed. pe Sa ne ree - EDINBURGH: Printed by A. Balfour. eee DIRECTION TO THE BINDER. The PLATE is to front the TrTLe. ee = e oy *, ute 9 F4) rp mlvns wg, SetyG mvthagas Pi Gn th eH OEE a terdere thas deers enin Crees am aia =a ON ttn mth ergs OP ee eemeentebyeieetenempapiet rigtsatphetseotsestcdeoniintGromses aentoueg oer ans oss . flpecbetegeostaden eee bepodairenaa pobneesedassbene imasbeindeloGeneree