LINNEAN SOCIETY OF LONDON. XV 



Though few zoologists will now be prepared to accept the conclu- 

 sions of the Genevan naturalist and his associates, the ccelenterate rela- 

 tions of the Infusoria have recently found an advocate in Greeff *. In 

 an elaborate memoir on the Vorticellce, Greeff sees in the very well- 

 marked distinction between the external or cortical layer and the in- 

 ternal soft body-substance, a proof of the views maintained by Claparede 

 and Lachmann ; and he considers this position still further 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 form, they 

 all possess a more or less close resemblance to the thread-cells of the 

 Ccelenterata. 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 ' f , Gegen- 

 baur expresses doubts as to the sexual nature of the reproductive 

 phenomena of the Infusoria, and is disposed to regard the so-called 

 embryo-sphere in the light of a proliferous stolon from which several 

 embryos 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 Acinetce, he believes that we are justified in 

 regarding the Acinetce as 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 Infusoria as affording evi- 

 dence 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 observa- 



* Greeff, " Untersuchungen iiber den Bau und die Naturgeschichte der Vorti- 

 cellen," Archiv fur Naturg. 1870. 



f Grundzijge der vergleichenden Anatomie, 1870. 



