595.18 43 



591.16 



IV 



The Progress of Research on the Reproduction 



of the Rotifera 



OF the numerous problems presented by the Rotifera, none are 

 more important than those connected with the complex 

 reproductive relations of these animals. The extreme degree of 

 sexual dimorphism, and the prevalence of parthenogenesis to the 

 probable exclusion, in some cases, of sexual reproduction, are striking- 

 features which, while not without parallel in other groups, can 

 nowhere be more conveniently studied. In spite however of the 

 great amount of attention which has been directed to the group, 

 many points in their life-history are still obscure, while some of 

 the most fundamental facts have only recently been definitely 

 ascertained. 



In Ehrenberg's great work on the Infusoria (1), from which our 

 exact knowledge of the group may be said to date, the Rotifera are 

 described as hermaphrodite, the convoluted excretory tubules having 

 been mistaken for the testes and their ducts. While it was soon 

 recognised by other observers that these structures had nothing to 

 do with reproduction, the view that the rotifers were hermaphrodite 

 appeared to be confirmed by Kolliker's (2) discovery of spermatozoa 

 within the body-cavity of Megalotrocha. Since the ovary and oviduct 

 are completely shut off from the body-cavity, it seemed obvious that 

 these spermatozoa must have originated where they were found, and 

 indeed Kolliker described them as developing from nucleated cells 

 in the body-cavity. The first known male rotifer was described in 

 1848 by Bright well (3) in the species afterwards named in his 

 honour Asplanchna hrightwelli. In the following year the same 

 species was made the subject of a careful monograph by Dalrymple 

 (4), who recognised the complete absence of the alimentary system 

 in the male. In 1857 P. H. Gosse, in a well-known paper (7), 

 described the males of ten species and indicated their probable 

 existence in several other forms belonging to distinct families of 

 the Rotifera. He affirmed the dioecious character of the group as 

 a whole, and compared the degraded anenterous males with those of 

 the Cirripedia which had then recently been described by Darwin. 

 In 1897 C. F. Rousselet (27) gave a list of nearly one hundred 

 species in which the male forms were known, and the number has 

 since been added to by Weber (29) and others. 



