TAIL-REUION OF POLTSTOTEEMA (pDELLOSTOMa) STOUT I. 309 
Studies on the Development of the Veno-Lym- 
phatics in the Tail-region of Polistotrema 
(Bdellostoma) stouti. First Communica- 
tion : Formation of the Caudal Hearts. 
By 
William F. AlUii. 
Publication No. 11 from the Zoological Laboratory of the University of 
Illinois, Urbana, Illinois. 
With Plates 19-21. 
I. Introduction. 
The purport of tliis and a following communication is to 
record certain facts and conclusions concerning* the origin of 
the veno-lymphatics in tlie tail region of .Polistotrema 
(Bdellostoma) stouti. This paper will include a descrip- 
tion of the adult condition of these vessels and the manner in 
which the caudal hearts are formed. Shortly I hope to follow 
with a second communication on the development of the veno- 
lymphatics in the tail region. 
For several years I have been gathering together a series 
of Polistotrema embryos from Monterey Bay, California. 
Miss Julia B. Platt of Pacific Grove, California, Prof. G. C. 
Price of Stanford University, and Miss Julia AVorthington of 
Cincinnati, Ohio, have generously added to my collection. 
All of the embryos were obtained by one Chinese hshernian, 
and unless someone was present to take charge of the 
material he was likely to preserve partly decayed embryos. 
Consecpiently a considerable portion of my material had to be 
discarded after sectioning; especially was this true of stages 
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