Developmental History of Infusorial, Animal Life. 369 



terized all attempts to explain anything like a generative 

 function in the Infusoria, we have substituted, by Balbiani, a 

 clear and complete survey of their leading phenomena. The 

 Infusoria have long been known to multiply by spontaneous 

 fissure, gemmation, and the production internally of various 

 formed bodies, which many observers have described under the 

 name of " embryos." The phenomena of " encysting," " con- 

 jugation," etc., which these minute bodies frequently exhibit, 

 and the relation, real or supposed, between such processes, 

 and their various modes of propagation, have from time to 

 time afforded matter for no little controversy. M. Balbiani's 

 investigations, however, derive additional interest from the very 

 complete manner in which they have been carried out. As 

 an instance of this, he states that in his examination of Para- 

 mcecium aurelice 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 reagents, 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. Balbianr's researches on 

 the phenomena of reproduction among the Infusoria, which 

 have added most valuable information to our former meagre 

 knowledge of these interesting forms of organic life. 



The case of the Infusoria is, in some respects, comparable 

 to the fertilization of Orchids, which Darwin has investigated 

 with so much care, and rendered doubly interesting by showing 

 how highly complicated are the contrivances by which among 

 this beautiful and extensive group of hermaphrodite plants, 

 fertilization is accomplished, and that, save in a few exceptional 

 instances, self-fertilization is almost impossible. Comparing 

 the Infusoria with Orchids, we may see that their fecundation 

 is effected by constant dissimilar elements produced in different 

 individuals ; and in both cases the details of the process are 

 curiously varied in their several tribes. 



In 1819 Chamisso detected the mode of reproduction of 

 the Biphorce, and coined the term, " Alternation of Genera- 

 tions."* He found that the isolated Salpce only produced 

 chained-salpaa, and then only by gemmation ; whilst the 

 chained-salpa8 produced isolated ones, and only by ova. The 

 discovery of the now well-known life history of the Medusce 

 was next made by Saars and Siebold; it was shown that the 

 Medusa aurita deposits an egg, which gives rise to a polyp, 



* This term is more generally associated with the name of Steenstrup, the 

 well-known author of a learned and valuable treatise on the subject. 

 VOL. X. — NO. V. B B 



