ON TUBIFEX RIVULORUM. 171 



The mature eggs collected in the matrix present the 

 appearance shewn in Fig. ii. The granular yelk is now formed, 

 and, I think, that the four or five eggs which are thus frequently 

 found to occupy one segment of the body, are deposited together 

 in one ovi-capsule, as we shall see further on. They escape, 

 according to Claparede, between the external wall of the atrium, 

 and its inner membranous one, and in order to make this a little 

 clearer, I have given in Fig. i8 a diagrammatic section of the 

 atrium across the Hne x x in Fig. 3, where it will be seen that the 

 oviduct thus formed has a circular section. It terminates in a 

 bulbous organ of a brown colour, and greater hardness than the 

 surrounding tissues ; and encloses within it the intromittent organ 

 which terminates the vas deferens. Both are placed within an 

 inversion of the integument which forms the sexual orifice, from 

 which however they can be exserted ; the intromittent organ also 

 can be exserted from within the bulbous termination of the 

 oviduct. These parts are shown in Fig. 3. 



The seminal receptacles found in the tenth segment are, in the 

 earliest condition in which I have recognised them, minute 

 sausage-shaped sacs, occupying but a small portion of the 

 segment in which they occur (Fig. 12). Subsequently they appear 

 as larger spherical sacs communicating, by a long neck, with the 

 external surface of the segment (Fig. 13). Like the vasa deferentia 

 they are, as Claparede remarks, specialised segmental organs. In 

 this condition I can distinguish in them an external epithelium 

 which extends along the duct, and which I look upon as a 

 continuation of the peritoneal lining. Within this is a muscular 

 layer of circular and longitudinal fibres, and the central cavity is 

 occupied by free epithelial cells, derived, I believe, from the 

 epidermis. At the period of their greatest development these 

 sacs frequently occupy, in addition to their own, the greater part 

 of the two segments adjoining that in which they originate. The 

 epithelial cells with which they were formerly occupied disappear, 

 and in their place we find the spermatophores introduced from the 

 male organs of another worm. These, according to Lankester, 

 are not introduced in the form in which they are found, but the 

 cementing substance, including the spermatozoa, is introduced in a 

 viscid form, and is subsequently moulded into shape within the 



