‘on one side of the body, as shown in the figure. At about its middle 
the tail splits into lamella-like paddles, and it is this divided tail 
=. that forms the most interesting feature of the larva, On each side-of 
; the anterior end of the larva is a mass of dark granular mass. The 
other bodies found in the interior of the larva are shown in the accom- 
panying figure. 
We never succeeded in getting more of these Cercaria, although I 
looked for them on several occasions.—T. H. MORGAN. 
| | 1891.] Embryology. | 1139 
t 
| 
Hatschek’s Interpretation of the Annelid Trochophore.— 
Zoologists and embryologists have looked forward with a good deal of 
interest to the publication of the third part of Dr. Berthold Hatschek’s 
“ Lehrbuch der Zoologie,” in which he gives what may be considered 
the most recent and certainly the most novel treatment of that very 
heterogeneous group, Vermes (Zygoneura Hatschek). 
More especially interesting is the treatment of the larval form of* 
the Annelids,—the Trochophore. This is ground that Hatschek has 
es himself covered very thoroughly, and his words must carry a great 
|: deal of weight along with them, whether his particular view be accepted 
e or not. 
i ‘‘The Trochophore is the characteristic larval form of the Zygo- 
neura. In structure, the Rotifers stand very near to the Trochophore, 
and the Turbellarians which only reach the stage of the Protrochula 
are very closely related to this last form. In many cases the charac- 
teristics of the Trochophore are more or less modified, or even entirely 
| suppressed, as happens in direct development. The primitive type of 
> the Trochophore may be determined by a comparison of those struc- 
f 


tures that are repeated in very widely separated groups of animals. A 
complete union of all the typical properties in a single larval form is 
perhaps never reached, still many Annelid larvæ approach very near 
to this.” A very clear and full description is given of a typical Tro- 
chophore. This is illustrated by four new diagrams, that show the 
structure of the larve most excellently. 
With respect to the phylogenetic interpretation of the Trochophore 
the author says: “‘ If we assume as true that the Trochophora is the 
characteristic form of the Scolecida, Articulata, Tentaculata, and 
Mollusca, we have recognized a common body for all these groups. 
We may also assume a common descent, and state the law that the 
_ Zygoneura are derived from a common ancestral form, that has tl e 
' Trochophora as a stage in the development. Further, we may ask 
the question whether the Trochophore is itself the repetition of a1 
} “ 3 BUN ae $ ` 





