174 ON TUBIFEX RIVULORUM. 



On one occasion I noticed that the eggs in the egg-cases were 

 sometimes filled with, as yet, unsegmented granular yelk. Others, 

 especially when submitted to the action of acetic acid, showed a 

 mulberry-like mass of cells, the morula, as Claparede states, but 

 this was confined more particularly to one side of the egg, and 

 some of the original granular yelk was still associated with it, as 

 seen in Fig. 1 7, « ; this I take to indicate a stage of yelk-division 

 preceding the formation of the blastoderm, and that the division 

 does not proceed equally in all parts, but that a portion is left 

 unsegmented, forming what is called food-yelk ; this being 

 gradually used up by the growth of the embryo. The yelk- 

 division, in fact, is what is termed incomplete. The addition 

 of glycerine instead of acetic acid renders the co-existence 

 of cellular and granular contents in the eggs at this stage very 

 clear, but the cells become separated from each other instead 

 of cohering in a mass as before (see Fig. 17, b). 



I cannot conclude this paper without quoting a passage from 

 Gegenbaur's Comparative Anatomy, which I have just seen, and 

 which seems to contradict Lankester's statement that the sperm- 

 atophores are formed within the seminal receptacles. He says 

 (p. 191): — "In many Annulata the seminal filaments are united 

 into masses of definite forms (spermatophores) in special parts of 

 the male efferent duds ; these are passed as such into the female 

 apparatus. Many Scolecina have spermatophores of this kind, 

 which are merely formed by agglutinated seminal filaments 

 (Tubifex)." As this was published in 1878, the author might be, 

 and very probably was, acquainted with Lankester's paper. 



EXPLANATION OF PLATES XXXIII. & XXXIV. 



Plate XXXIIL 

 Fig. 1. — Diagram representing the position of reproductive organs of 

 Tubifex, according to Claparede. The segments are marked 

 with Roman numerals. <., the testes; ov., the ovaries; om, 

 mature ova in matrix ; /. , the funnels ; i.e., the ciliary tube ; 

 at, the atrium; s.o. , the sexual orifice; v.s. , vesica semi- 

 nalis ; s.7'. , the seminal receptacles ; i. , the intestine. 

 ,, 2. — Fusiform fibres of ciliary tube (Clap). 



