595.18 43 
591.16 
IV 
The Progress of Research on the Reproduction 
of the Rotifera 
F 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, ‘ean 
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 Brightwell (8) in the species afterwards named in his 
honour Asplanchna brightwelli. 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. 
