410 THE MICROSCOPE. 



constricted, and here is a slit seen which, opens into a little 

 funnel-shaped cavity, leading to the gullet and stomach. 

 The outer or cortical layer is composed of a denser ma- 

 terial, which indicates a differentiation into cellular layers, 

 while the internal substance is evidently composed of 

 sarcode which exhibits, at two points in particular, the 

 power of contracting and dilating : a process available both 

 for the expulsion of digested food, and for aeration of the 

 circulatory system. The whole systemic arrangement 

 should be regarded as the very simplest form of respiratory 

 and secretory mechanism. The several circular trans- 

 parent bodies seen in the interior of these animals led 

 Ehrenberg to denominate the group " Polygastrica " (many 

 stomached). The remarkable powers of multiplication by 

 fission and germination, as well as by a true sexual process, 

 which these creatures exhibit, have attracted the attention 

 of all observers; within the last few years, Muller, 

 Balbiani, Stein, and others, have shown that the sexual 

 organs of such animals as Paramecium are those bodies 

 which have hitherto been simply regarded as the 

 " nucleus," and "nucleolus ; " and ultimately it was seen 

 that the Infusoria have a life history as wonderful as that 

 of the higher classes of animals. Although Ehrenberg 

 was the first to call attention to the importance of the 

 " nucleus " in the reproductive process, it is to the observa- 

 tions of Balbiani that we are indebted for an explanation of 

 its importance in the generative function : his investiga- 

 tions also derive additional interest from the very complete 

 manner in which they have been carried out. As an in- 

 stance, he states that in his examinations of Parametrium 

 aurelia?, he could not look upon them as conclusive until 

 he had succeeded in extracting uninjured some of the eggs 

 from the parent body, and had subjected them to the 

 action of the surrounding water, when he saw each egg 

 resolve itself into two portions, the smaller being enclosed 

 within the larger ; then by employing re-agents, acetic acid 

 and iodine, he produced the changes more rapidly ; and in 

 this way again and again obtained abundant proofs of the 

 truth of each observation. So much then for Dr. Bal- 

 biani's researches on the phenomena of reproduction 

 among the Infusoria, which have added much valuable 



