132 WHITMAN. [Vol. I. 



mine the special part which each plays in the formation of the 

 embryo. Although he has thus left it impossible to distinguish 

 the different kinds of teloblasts, we may safely assume that they 

 represent mesoblasts, neuroblasts, and nephroblasts, and that 

 they all originate from the large posterior macromere. Allow- 

 ing that the teloblasts are here similar in origin and character to 

 the teloblasts of Clepsine, Nephelis, and Lumbricus, it follows 

 that the entoderm must arise, chiefly at least, from the other 

 three macromeres. The chief difference, then, between Branchi- 

 obdella and Clepsine, in respect to the entoderm, would lie not 

 in the source, but in the mode of origin. In the former the 

 cleavage process is continued to the end, while in the latter it 

 ceases with the formation of the primary macromeres, the work 

 then being completed by the intermediation of entoplasts. 



In regard to the extent to which the epithelium of the ali- 

 mentary canal is of entodermic origin, Salensky remarks (p. 

 56) : " Ce canal tout entier, a I'exception des parties insigni- 

 fiantes avoisinant la bouche et I'anus, est exclusivement forme 

 par I'entoderme." Speaking of the oesophagus, he says (p. 58) : 

 " Le processus de revolution de I'oesophage, chez Branchiob- 

 della, demontre clairement que tout I'epithelium de cette partie 

 nait exclusivement aux depens de I'entoderme." The same 

 will be shown to hold true in Clepsine. 



Salensky (No. 15, p. 19) has misunderstood my statements 

 with reference to the relation of the embryonic axis to the 

 main axis of the egg. The cephalic lobe is very nearly cen- 

 tred on the upper pole of the egg in Clepsine, and the mouth 

 arises at, or at least very near, this pole. It does not follow, 

 however, that because the mouth is located at the oral pole, 

 the posterior end of the embryo must be found at the opposite, 

 or aboral pole. A glance at my figures will show that the 

 two ends of the embryo are at first very near together, the cau- 

 dal end itself lying just behind the area occupied by the four 

 primary micromeres. The axis of the embryo may, therefore, 

 be said to be at right angles to that of the Qg^, as it is in 

 Branchiobdella and Nephelis.^ 



' I cannot agree with Salensky that the embryology of Branchiobdella establishes 

 its title to be ranked among the Hirudinea. Both its development and adult structure 

 appear to me to sustain the opinion, now held by most authorities, that it stands 

 nearer the Oligochseta than the Hirudinea. 



