June 20,, 1875] 



NATURE 



155 



RECENT PROGRESS IN OUR KNOWLEDGE 

 OF THE CILIATE INFUSORIA* 

 II. 

 'T'HE reproductive process was lately followed by myself 

 •*• through some of its stages in a very beautiful Vorticellidan 

 obtained abundantly from a pond in Brittany, t The zooids which 

 form the colonies in this Infusorium are grouped in spherical 

 clusters on the extremities of the branches. They present near 

 the oral end a large and very obvious contractile vesicle, and 

 have a long cylindrical nucleus curved in the form of a horseshoe. 



In the internal protoplasm are also imbedded scattered green 

 chlorophylloid granules. No trace ef the so-called nucleolus was 

 present in any of the specimens examined. 



Among the ordinary zooids there were usually some which had 

 become encysted in a very remarkable way, and without any 

 previous conjugation having been noticed. These encysted forms 

 were much larger than the others and had assumed a nearly 

 spherical shape ; the peristome and cilia-disc had become entirely 

 withdrawn, the contractile vesicle was still obvious, but had 

 ceased to manifest contractions j brownish spherical corpuscles 

 with granular contents, probably the more or less altered chloro- 

 phylloid granules ot the uncncysted zooid, were scattered through 

 the parenchyma, and the nucleus was not only distinct, but had 

 increased considerably in length. Round the whole a clear 

 gelatinous envelope had become excreted. 



In a later stage there was formed between the gelatinous enve- 

 lope and the cortical layer of the body a strong, dark -brown, 

 apparently chitinous case, the surface of which in stages still 

 further advanced had become ornamented by very regular hexa- 

 gonal spaces with slightly elevated edges. In this state the chi- 

 tinous envelope was so opaque that no view could be obtained 

 through it of the included structures, and in order to arrive at any 

 knowledge of these it was necessary to rupture it. The nucleus 

 thus liberated was found to have still further increased in 

 length, and to have become wound into a convoluted and com- 

 plicated knot. Along with the nucleus were expelled multi- 

 tudes of very minute corpuscles with active Brownian movements. 



In a still lurcher stage the nucleus had become irregularly 

 branched, and at the same time somewhat thicker and of a 

 softer consistence ; and finally, it had become broken up into 

 spherical fragments, each with an included corpuscle resembling 

 a true cell nucleus in which the place of a nucleolus was taken 

 by a cluster of minute granules. 



In this case the original nucleus of the Vorticellidan had thus 

 become broken up into bodies identical with the so-called eggs 

 of Balbiani, but this was unaccompanied by any conjugation or 

 by the formation of anything which could be compared to 

 spermatozoal filaments. 



What I believe we may regard as now established in the 

 phenomena of reproduction in the Infusoria is, that besides the 

 ordinary reproduction by spontaneous fission of the entire body, 

 the nucleus at certain periods, and after more or less change of 

 form has occurred in the Infusorium body, becomes broken up 

 into fragments, each including a corpuscle resembling a true cell 

 nucleus ; and that this takes place without necessarily requiring 

 the influence of conjugation or the action of spermatozoa ; that 

 these fragments after their liberation from the body of the In- 

 fusorum become developed— still without the necessity of sper- 

 matic influence — directly or indirectly into the adult form. 



Whetlier proper sexual elements ever take part in the life 

 history uf the Infusoria remains an open question. 

 \.. Everts t has given an account of observations which, with the 

 view of testing the statements ot Greeff, he made on Vortkella 

 nebulijera. Greeff, as we have seen, followed Claparcde and 

 Lachmann in attributing to the Vorticellae a true ccelenterate 

 structure j and Everts, by his own investigations, has convinced 

 himself of the untenabltness of this view, and has been led to 

 regard the Vorticellse as strictly unicellular. 



He recognises the distinction between the cortical layer (which 

 forms not only the periphery of the body but the whole of the 

 stalk on which this is supported), and the central mass in which 

 the nutriment is deposited, collected into pellets and digested ; 

 but instead of regarding this central mass as chyme, he looks 

 upon it as an integral constituent of the entire body, like the 

 cential portion 01 an Amceba. The nucleus is imbedded in the 



* Anniversary Address to the Linnean Society, by the President, Dr. G, 

 J. AUman, t.K.S., May 24. Continued from p. 137. 



t British Association Reports, 1873. 



i Everts, Untcrsuchungen an Vorticella nebuli/era. Sitzungsberichtc 

 der Physikalisch-Medicinischen SocieUt zu Erlangen. 1873. 



inner side of the cortical layer, which Is itself differentiated into 

 certain secondary layers. He describes the deeper part of the 

 cortical layer as exhibiting a rotation of its granules independent 

 of the rotation which occurs in the central parenchyma, and 

 moving in a direction opposite to that of the latter. Everts's 

 account of the structure of Vorticella is thus in accordance with 

 the conception of it as a cell with a parietal nucleus ; a cell, 

 however, in which differentiation is carried very far without the 

 essential character of a simple cell being thereby lost. 



Everts regards the external wall as corresponding with the 

 ectoderm, and the internal softer body-substance with the endo- 

 derm of higher animals. If by this the author meant to indicate 

 a honiological identity between the structures thus compared, it 

 is plain that he would have taken an entirely mistaken view 

 based on a misconception of the essential nature of an ecto- 

 derm and endoderm. These membranes are essentially multi- 

 cellular, and are always results of the segmentation of the vitellus 

 in a true ovuin. They can therefore never be attributed to a 

 unicellular animal, in which no true segmentation process ever 

 takes place. In his rejoinder, h»wever, to an elaborate criticism 

 of his memoir by Greeff, he explains that he intended to com- 

 pare the two layers of the Infusorium body analogically, not 

 morphologically, with an ectoderm and endoderm. 



The same author has further made some interesting observations 

 on the development of Vorticella. He has noticed that reproduc- 

 tion is here ushered in by a longitudinal cleavage, in which after 

 division of the nucleus the body of the Vorticella becomes cleft 

 into two halves, still seated on the common stalk. Each of these 

 develops near its posterior end a wreath of vibratile cilia, while 

 the peristome and the cilia-disc over the mouth are entirely with- 

 drawn, and then breaks loose from its stem and swims freely 

 away. These free-swimming Vorticella; now encyst themselves, 

 the cilia disappear, and the contents of the encysted animal 

 acquire a uniform clearness with the exception of the nucleus, 

 which persists unchanged. In the next place the nucleus breaks 

 up into eight or nine pieces, and then the wall of the cyst 

 becomes ruptured and gives exit to these fragments, which now 

 appear as spontaneously moving spherules. These increase in 

 size, develop on one end a cilia wreath, within which a mouth 

 makes its appearance, and the free-swimming nucleus-fragment 

 becomes gradually changed into a form which entirely agrees 

 with the Trichodina grandmdla of Ehrenberg. 



These Trichodinas now multiply by fission, first developing a 

 posterior wreath of cilia, and then dividing transversely between 

 the anterior and posterior wreaths. After this each fixes itself 

 by the end on which the mouth is situated ; a short stem 

 becomes here developed, and the cilia wreath gradually dis- 

 appears. Then upon the free end the peristome and cilia disc 

 make their appearance, and the growth of the stem completes 

 the development. 



Everts remarks that in this process we have an example 01 

 alternation of generations. There is one point, however, in 

 which he has overlooked its essential difference from a true 

 alternation of generations, namely, the absence of any intercala- 

 tion of a proper sexual reproduction. 



Ray Lankester * has subjected to spectrum analysis the blue 

 colouring matter of Stenior carulens. This occurs in the form of 

 minute granules in the cortical layer of the animal, and Lan- 

 kester finds that it gives two strong absorption bands of remarkable 

 intensity, considering the small quantity of the matter which can 

 be submitted to examination. He cannot identify these bands 

 with those of any other organic colouring matter, and to the 

 peculiar pigment in which he finds them he gives the name of 

 sUniorin. 



He has also examined the bright green colouring matter ot 

 Stentor Mulleri, and finds that instead of giving the steptorin 

 absorption bands, it gives a single band like that of the chloro- 

 phylloid matter of Hydra viridis and of Spongilla. 



Ray Lankester t has also described, under the name of Tor- 

 quatella typica, a remarkable marine Infusorium, which, though 

 quite destitute of true cilia, can scarcely be separated from the 

 proper Ciliata. With the general structure of the ciliate 

 Infusoria, the place of a peristomal cilia wreath is taken by a 

 singular plicated membrane, which forms a wide, frill-like, very 

 mobile appendage, surrounding the oral end of the animal, and 

 projecting to a considerable distance beyond it. The author 

 regards 'Jorquatella iypica as the type of a distinct section of the 

 Ciliata to which he gives the name of Calycata. 



Of all the authors who since Von Siebold have applied themselves 



* Quart. Joum. Mic.Sci., 1073. f Ibid. 1874. 



