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Übersetzungsrecht vorbehalten. 
The spermatogenesis of Hydra. 
By 
E. R. Downing, Marquette (Mich. U.S. A.). 
With plate 22—24. 
Introduction. 
Hydra and the coelenterates have occupied a conspicuous place 
in the development of biological theory. The first experiments on 
regeneration were performed on hydra. It and other coelenterates 
have been subjects of many investigations looking to the settlement 
of the gastraea theory and the mooted germ layer hypothesis. Wuts- 
MANN obtained his evidence for continuity of the germ plasm largely 
from investigation of this group. While therefore there is much 
literature on the ovogenesis and spermatogenesis of the coelenterates, 
it is nearly all for the express purpose of simply determining from 
which germ layer the sex cells are derived; very little has been 
done in following the nuclear changes during spermatogenesis and 
nothing has been published on the reduction phenomena of this or 
the lower groups of animals. The present study was undertaken 
to determine if in so simple an animal as Hydra there occurs any 
simplification of the process of spermatogenesis as known in the 
higher animals. 
Historical. 
In 1743 Baker (2) published a drawing of Hydra with testicles. 
This is reproduced in Fig. 1. It is the first mention of these organs 
Zool. Jahrb. XXI. Abt. f. Anat. 25 
