172 ON TUBIFEX RIVULORUM. 



sac itself. A drawing of one of these curious objects will be 

 found in Plate 33, Fig. 4. 



Sometimes the conical head is wanting, which results from the 

 spermatophore being moulded lower down in the sac. The 

 spermatozoa are disposed spirally within the matrix, from the 

 surface of which they project, and maintain a constant ciliary 

 action, giving the spermatophore the appearance of a nondescript 

 ciliated infusorium. It is very curious that the movements of a 

 number of perfectly independent vital elements should be so 

 correllated as not only not to clash with each other, but to re- 

 produce all that regularity of movement, which is seen where the 

 ciliated surface forms part of one organic whole. Perhaps, 

 however, remembering the separate vitality of the cell elements of 

 the simplest protophytes, as well as of higher forms, both of 

 animal and vegetable life, the only really curious thing is, that this 

 rhythmical movement is reproduced as perfectly when the ciliated 

 cells, originally separate, are brought together by a mechanical 

 process, as when their juxtaposition arises through the ordinary 

 processes of cell multiplication and growth. The ciliary action 

 takes place in a series of waves, which follow each other over the 

 surface of the spermatophore like the advancing threads of a 

 screw (see Fig. 15). It is only on one or two occasions, however, 

 that I have been enabled to see this phenomenon, as it is com- 

 paratively rarely that the spermatophores are found in an active 

 condition. In by far the majority of specimens they appear to be 

 exhausted, and in various stages of absorption ; the spermatozoa, 

 as I suppose, having worked their way out of the matrix, and the 

 question now arises, what becomes of them ? I have never been 

 able to discern them in a free condition in the receptacles, 

 although Claparede states that he has sometimes found them there. 



The subject now appears to be encompassed with difficulties 

 which Lankester's paper does not deal with, or even allude to. 

 In some way or other it may be presumed the spermatozoa, having 

 freed themselves from the spermatophore, and finding themselves 

 within a sac-like receptacle whose only opening is external, have 

 to make their way to the ova of the worm in which they are 

 found. The receptacles, it will be remembered, are in the tenth 

 segment, and the ovaries in the eleventh. To escape by the orifice 



