564 FRESH-WATER BIOLOGY 



The organs of reproduction are still to be considered. Most of 

 the rotifers commonly seen are females, as the males are very 

 minute and rare. In the Notommatidae, as in most other rotifers, 

 there is a single large reproductive body, commonly spoken of as 

 the ovary, or sometimes as the germarium. This lies ventral to the 

 intestine, in the posterior third of the body (Figs. 856 and 857, ov). 

 It consists of two portions, of different functions. The large part 

 contains a small number of large nuclei, often just eight; this por- 

 tion prepares the yolk for the developing egg, so that it is called 

 the vitellarium. At one end or side of this vitellarium is a small 

 mass containing many minute nuclei. From this part the egg 

 develops, the small nuclei becoming each the nucleus of an egg. 

 This part is known as the germarium, since it produces the egg or 

 germ. From the ovary a thin-walled, sac-like passageway, the 

 oviduct, leads backward to the cloaca; by it the egg is discharged. 

 The oviduct can be seen, as a rule, only with great difficulty. 



In most rotifers the males are small and degenerate. But in 

 some of the Notommatidae, as well as in a few other species, they are 

 nearly as well developed as the females, and resemble them in 

 structure. In Proales werneckii (Fig. 856), which hves within Vau- 

 cheria filaments, the male is as large as the female, but the ali- 

 mentary canal is not quite so well developed. In Rhinops vitrea 

 (Fig. 863), the male is smaller than the female but not otherwise 

 degenerate, while in the aberrant rotifers known as the Seisonacea 

 males and females are alike, save for the reproductive organs. In 

 most other rotifers the minute males either lack the alimentary 

 canal entirely or have only vestiges of it (see Fig. 864). In all 

 cases in the male in place of the ovary is found a sac, the sperma- 

 rium {sp), in which many spermatozoa are seen swimming about. 

 The sac extends backward as a large tube, ending in a ciliated 

 opening from which the spermatozoa are discharged. That por- 

 tion of the tube bearing the opening may be protruded as a copu- 

 latory organ. 



The chief structures of a typical rotifer have now been described, 

 mainly as shown in the Notommatidae. Next, the Rotifera as a 

 whole will be surveyed and the different groups examined rapidly 

 to note how these differ from the notommatids and from one an- 



