ON THE REPRODUCTIVE SYSTEM IN THE HYDROIDA. 383 
while the head varies in form, being usually conical—and then with the 
filament attached to the wide end of the cone,—but sometimes spherical, or 
eylindrical, or ‘‘ guitar-shaped”’*, according to the species. 
The spermatozoa seem to be always developed in true sperm-cells which 
are themselves frequently contained as a brood in the interior of mother cells, 
as may be very well seen in Sertularia polyzonias, where the cells which give 
immediate origin to the spermatozoa form groups of from two to four enclosed 
within a common mother cell. The spermatozoon itself seems due to the 
metamorphosis of the nucleus of the sperm-cell. 
In Laomedea flexuosa I have carefully followed the progress of the sper- 
matogenous tissue from a very early period to the formation of the mature 
spermatozoon. In the very young gonophore (fig. 14 A) the spadix may be _ 
here seen surrounded by a nearly transparent mass, which is destined to be- 
come developed into spermatozoa, but which presents as yet no obvious struc- 
ture beyond a minutely granular condition, which under the action of acetic 
acid becomes more distinct. 
In a stage a little further advanced (B) the gonophore has increased in size, 
and the spermatogenous mass has become more voluminous and has acquired 
Fig. 14.—Development of the spermatozoa in Laomedea fleauosa, 
Cc 
CG wy Cx 9000%5 
J0 @® $ 
a 6 \ 
a 
A, very young male gonophore bud, with the spermatogenous plasma interposed between 
the ectoderm and endoderm; B, gonophore further advanced ; C, mature gonophore ; 
D, structure of spermatic tissue at various stages. @, spermatic tissue from B; 8, the 
same, after having been treated with acetic acid; c, spermatic tissue from a gonophore 
somewhat further advanced than B ; d, mature spermatozoa from C. 
a manifest structure, being now plainly formed by a peculiar tissue which, 
when liberated from the confinement of the gonophore and spread over the 
* The spermatozoa of Hudendrium dispar, Agassiz, and some other species are so de- 
seribed by Agassiz in Nat. Hist. of the United States, vol, iv. 
