The spermatogenesis of Hydra. 415 
structure, it seems more likely a primitive than a degenerate type. 
The absence of migration in the sex cells of Hydra while such 
migration is universal in the medusoid polypes would seem to add 
to the probability. The sex cells originally existing in each simple 
polyp would naturally in a complex colonial form migrate to those 
individuals which had assumed the reproductive function. 
I desire to express my appreciation of the help and inspiration 
given me by Dr. C. O. Wurrman in the pursuance of these studies. 
Note. Since the completion of this paper there have appeared 
two papers by Konrap GUENTHER on this subject; „Die Samenreifung 
bei Hydra viridis“, in: Zool. Anz. V. 26, No. 705, p. 628—630 and 
„Keimfleck und Synapsis, Studien an der Samenreifung von Hydra 
viridis“, in: Zool. Jahrb., Festschrift f. Weismann, 1904. GUENTHER’S 
research was undertaken to derive evidence on a previously conceived 
theory regarding the function of the nucleolus. This is not an 
appropriate place to discuss that theory but there are some im- 
portant matters of observation on which we differ that need comment. 
GUENTHER maintains that the spermatogonia are derived from 
the ectoderm cells, but gives no proofs other than his figures. In 
these the so called ectoderm cell, fig. 6a, is smaller than the 
spermatogonium fig. 1—6. The difference in size of ectoderm cells 
and interstitial cells shown in my Figs. 12 and 15 and the fate 
of the ectoderm cells of the spermary shown in Fig. 9 and described 
in the text seem to me to disprove this hypothesis. 
He points out the importance of the disappearance of the cell 
wall. In my preparations, the cell walls are perfectly distinct. 
Hydra viridis was found more difficult to fix than the other species 
and was not used as extensively in consequence. 
EK. R. Downine. 
The Peter White Hall of Science 
Northern State Normal School 
Marquette, Mich. U.S. A. 
