yune 17, 1875] 



NATURE 



137 



cleavage had in many cases an entirely different significance ; 

 that it was, in fact, not the cleavage of a single individual, but 

 the conjugation of two distinct ones; and he connected this 

 phenomenon with what he regarded as a true sexual act. 



It was then known that besides the nucleus which occupied a 

 conspicuous position in the protoplasmic mass, there existed in 

 many Infusoria another differentiated body similar to the nucleus 

 but smaller, and either in close contact with it or separated 

 from it by a greater •r less interval. To this body the 

 ill-chosen name of " nucleolus" had been given. Now, Bal- 

 biani's observations led him to believe that under the influ- 

 ence of conjugation this so-called nucleolus underwent a 

 change and developed in its interior a multitude of exceedingly 

 minute filaments or rod-like bodies, to which he attributed the 

 significance of spermatozoa ; while at the same time the nucleus 

 became divided into globular masses, which Balbiani regarded 

 as ^gs, and in which he believed he could recognise a germinal 

 vesicle and germinal spot. We should thus, according to this 

 interpretation, have in the Infusoria the two essential elements 

 of sexual differentiation, the spermatozoa and the egg. 



Stein, though differing from Balbiani in certain details, 

 accepts in its general facts the sexual theory, and maintains the 

 spermatic nature of the rod-like corpuscles to which the nucleolus 

 appears to give rise. But however real may be the phenomena 

 described by Balbiani and by Stein, the correctness of assigning 

 to them a sexual significance may be called in question ; and it 

 is certain that subsequent observation has not tended to confirm 

 the hypothesis that we have in the Infusoria true eggs fecundated 

 by true spermatozoa. 



Claparede and Lachmann, two able and indefatigable ob- 

 servers fresh from the school of the great anatomist Johan 

 Miiller, now entered the field, and their joint labours have given 

 us a great work on the Infusoria.* In this an entirely new view 

 of the morphology of the Infusoria has been introduced. Re- 

 ceding widely from the unicellular theory of Siebold, they 

 approximate towards the views of Ehrenberg in assigning to the 

 Infusoria a comparatively complex structure ; but instead of 

 adopting the polygastric theory of the Prussian microscopist, 

 they attribute to the Infusoria a single well-defined gastric cavity 

 occupying the whole of the space hmited externally by the outer 

 firm boundary walls of the softer protoplasmic mass ; while this 

 mass is regarded by them as nothing more than a sort of chyme 

 by which the gastric cavity is filled. According to this view, 

 the nearest relations of the Infusoria would be found among the 

 zoophytes, and their proper systematic seat would be in the 

 primary group of the Coclenterata. 



Though few zoologists will now be prepared to accept the 

 conclusions of the Genevan naturalists, the ccelenterate relations 

 of the Infusoria has recently found an advocate in Greeff.f In 

 an elaborate memoir on the Vorticellse, Greeff sees in the very 

 well-marked distinction between the external or cortical layer 

 and the internal soft body-substance, a proof of the views main- 

 tained by Claparede and Lachmann ; a»d he considers this 

 position still lurther confirmed by the presence in Epistylis 

 flavicans of numerous oval or piriform, brilliant, well-defined 

 capsules, which are generally distributed in pairs below the outer 

 layer, and which, under the influence of a stimulus, emit a long 

 filament, thus closely resembling the thread-cells so well known 

 as characteristic elements in certain tissues of the Ccelenterata. 



It must be here remarked that the presence of similar bodies 

 in the Infusoria, where they have been described under the 

 name of trichocysts, has long been known. Though varying in 

 fcrm, they all possess a more or less close resemblance to the 

 thread-cells of the Coclenterata. Their presence undoubtedly 

 indicates a step upwards in the differentiation of the organism, 

 but, as we shall presently see, it offers no valid argument against 

 its unicellularity. 



In his admirable " Principles of Comparative Anatomy,"! 

 Gegenbaur expresses doubts as to the sexual nature of the 

 reproductive phenomena of the Infusoria, and is disposed 

 to regard the so-called embryo-sphere, to which the nucleus 

 gives rise, in the light of a proliferous stolon, from which 

 several zooids are in some cases thrown off. Arguing from the 

 Acineta-like form of the young in the higher Infusoria, as 

 shown by Stein, and comparing the transitory condition of 

 this with the permanent condition of the true Acineta;, he 



* Claparede et Lachmann, " Etudes sur les Infusoires et les Rhizopodes." 

 Geneve, 1858-61. 



t Greeff, " Untersuchungen iiber den Ban und die Naturgeschichte der 

 Vorticellen." Archiv fur Naturg., 1870. 



X " Grundsiige der Vergleichenden Anatomic," 1870. 



believes that we are justified in regarding the Acineta; z.% the 

 ancestral form from which the proper Infusoria have been 

 derived. He further compares the contractile vesicle and its 

 canals in the Infusoria with the water vascular system of the 

 worms, and believes that a parentage with these higher forms 

 is thus indicated. Gegenbaur, moreover, expresses himself 

 strongly against the unicellular theory. He regards, however, 

 the absence of distinct cell nuclei in the substance of the Infu- 

 soria as affording evidence of their composition out of several 

 " Cytodes" or non-nucleated protoplasm masses rather than out 

 of true nucleated cells. 



Still more recently Biitschli has given us the results of obser- 

 vations on the conjugation of Paramc^cium aurelia. * He is led, 

 however, to doubt the vaUdity of the sexual interpretation of 

 the conjugation. He found that in certain cases in Paramcccium 

 aurclia and in P. colpoda the so-called spermatic capsule into 

 which the nucleolus had become converted, had entirely dis- 

 appeared without any evident change in the nucleus ; and he 

 concludes that fecundation of the bodies regarded by Balbiani 

 as eggs cannot be here entertained. Indeed, he will not allow 

 that we have evidence entitling us to regard the appearance of 

 filaments in the interior of the nucleolus as aftording any indi- 

 cation of true spermatozoa. He offers no explanation of this 

 appearance, but he calls attention to the fact that both Balbiani 

 and Stein noticed that in transverse division of the Infusoria — a 

 phenomenon with which conjugation can have nothing to do — the 

 nucleolus frequently enlarges and acquires a longitudinal striation 

 like that of the nucleolus in the supposed production of sperma- 

 tozoa during conjugation. Balbiani maintains that this striation 

 during cleavage is only superficial, but it nevertheless affords an 

 argument against assigning any more important significance to 

 the very similar appearance in the case of conjugation. 



On the whole it would appear that the spermatozoal nature ot 

 the stria; visible in the nucleolus of the conjugating individuals 

 — even admitting that these striae represent isolatable filaments — 

 has not by any means been proved, while the phenomenon of 

 conjugation in the Infusoria would seem to correspond rather 

 with the conjugation so well known in many lower organisms, 

 where it takes place without being in any way connected with 

 the formation of true sexual products. 



In the same memoir the results of observations on some other 

 points in the structure and economy of the Infusoria have also 

 been given by Biitschli, He records the occurrence of minute 

 crystal-like lamina; in the interior of a marine Infusorium (Slrovi- 

 biduan sulcatum) rendered remarkable by a conspicuous girdle 

 of trichocysts which surround its body. The crystal-like cor- 

 puscles seem to be of the nature of starch, for on the application 

 of iodine they assume a beautiful violet colour. It does not 

 appear from Biitschli's account of these bodies that they have 

 not been introduced from without, and the chief interest of the 

 observation seems to be in the discovery of an amyllaceous body 

 assuming a crystalline form. He had previously met with 

 similar bodies in a parasitic Infusorium (Nyctotherus oralis), as 

 well as in a Gregarina {G. blattarum). 



He also describes, under the name oi Polykricos S-cuartzii, a 

 new Infusorium which he frequently found in the fjords of the 

 south coast of Norway and in the Gulf of Kiel, and which he 

 regards as especially interesting, from the fact that with a true 

 infusorial organisation it contains, irregularly distributed in the 

 outer layer of the body, numerous capsules indistinguishable 

 from the true ccelenterate thread cells. These bodies, however, 

 are never included in a special investment, and he justly regards 

 their presence as affording no argument against the unicellular 

 nature of the Infusoria, He lays it down as a probable distinc- 

 tion between the trichocysts of the Infusoria and genuine thread- 

 cells, that the former have the power of ejecting their contained 

 filament from both ends of the capsule, while we know that in 

 the thread cell it is only one end which gives exit to it. This 

 double emission of a filament appears to have been observed by 

 Biitschli in the trichocysts of a large Nassula, but the distinction 

 is certainly not a generally valid one. There is no doubt that in 

 the majority of cases the trichocyst emits its filament from only 

 one end of its capsule, exactly as in the thread cells of the 

 Coclenterata, and it is hard to see in what respect the bodies 

 noticed by Biitschli in his Polykricos Swartzii essentially differ 

 from true infusorial trichocysts. In conlusion, he declares him- 

 self strongly in favour of the unicellularity of the Infusoria. 

 (To ie contintud.) 



* O. Biitschli, "Einiges fiber Infusorien." Archiv i. Microscop. Ailat., 

 »873. « 



