xiv REPRODUCTIVE ORGANS 403 



Female Reproductive Organs. The ovaries of the Hiru- 

 dinea appear to differ from those of the Oligochaeta in that the 

 ovaries are continuous with their ducts. In Hirudo, however, 

 the real ovary of each side consists of masses of germinal tissue 

 lying freely within a sac which communicates with a duct ; the 

 two ducts unite to form a much convoluted tube which opens 

 into a thick-walled vagina, itself opening again on to the exterior 

 by a median unpaired opening on the seventh segment. The 

 muscular vagina is not always present. 



The median unpaired female aperture offers now no particular 

 difficulty, since in many earthworms, e.g. Perichaeta, this orifice 

 is in the same condition ; nor does the fusion of the oviducts 

 and the so-called ovaries ; for in JEudrilus, for example, and in 

 many Eudrilidae, the ovary is contained in a sac into which the 

 oviduct also opens. It will be noticed too that the existence of 

 short oviducts as compared with the long sperm-ducts is a 

 further point of likeness to at any rate the higher Oligochaeta. 

 But a further comparison needs first to be based upon a con- 

 sideration of the development of the different sections of the 

 apparatus in the leech. The independence of the ovaries and 

 their ducts has been proved by several observers ; quite recently 

 Burger has dealt with the matter in JVephelis, Hirudo, and 

 Aulastomum gulo} He has found that the ovaries arise from 

 the splanchnic wall of the lateral coelomic cavities ; they are 

 therefore proliferations of the coelomic epithelium, as in Oligo- 

 chaeta and all Coelomates so far as is known. The peripheral 

 layer of the mass of indifferent cells which constitutes the 

 ovary becomes somewhat modified ; its cells are flattened, and 

 it at length separates itself and forms a capsule surrounding 

 the other cells, which are in fact, or become, the ovary. This 

 capsule meets and fuses with the ducts, which are invaginations 

 from the exterior of the body. 



There are clearly differences between the ovary of a leech and 

 . that of a typical Oligochaete like Lumbricus. The only point of 

 agreement, in fact, is the origin of the reproductive gland itself 

 from the walls of the body-cavity. In Lumbricus and allied 

 forms, whatever may be held with regard to their homo- 

 logies, the oviducts as a matter of fact appear first as funnels, 

 which afterwards bore their way to the exterior. They are 



1 Zeitschr. wiss. Zool. lyiii. 1894, p. 440 ; and Zool. Jahrb. Anat. iv. 1891, p. 697. 





