384. REPORT—1863. 
field of the microscope, is seen to consist of a multitude of bodies of a rather 
irregularly pyriform or conical shape, and about ;,),;th of an inch in diameter 
(Da). These bodies, when set free, present for the most part an evident 
vibratory movement, which is plainly a vital phenomenon, and distinct from 
mere molecular motion, though as yet no filament or other source of the 
motion can be detected. When treated with acetic acid, they assume a re- 
gularly spherical form, and have then all the appearance of thick-walled cells 
with an undoubted nucleus in their interior (D 6). 
In a more advanced stage the contents of the gonophore have still further 
increased in opacity, and are now seen to be entirely composed of very minute 
spherical corpuscles (D c) about 5,1,;th of an inch in diameter, and presenting 
a close resemblance to the nuclei of the cells composing the spermatogenous 
tissue in the stage last described. They exhibit distinct but not active mo- 
tion under the microscope, though no filament can as yet be demonstrated in 
them. 
In the next stage (C) the gonophore has attained maturity, and the sperma- 
togenous mass has become still more opake than in the preceding stage, and 
presents a peculiar striated appearance, the strie radiating from the sides of 
the spadix to the walls of the gonophore., Soon after the gonophore has at- 
tained this condition it bursts, and allows its contents to escape into the sur- 
rounding water as mature active spermatozoa (Dd). These spermatozoa have 
an ovo-conical head, with a caudal filament of extreme tenuity ; the head is 
about = ;'55th of an inch in its longer diameter, and about ;;1,,th in its shorter. 
The tail is attached to the wide end. 
In attempting an interpretation of the above appearances, we must, I 
think, regard the nucleated cells which constitute the contents of the gono- 
phore in the second of the stages just described as spermatic cells which in 
the next stage have set free their nuclei; these nuclei, after liberation from 
the cells, acquiring a more elongated form, developing a filament, and becoming 
converted into true spermatozoa. 
Allusion has been just made to the peculiar striated appearance presented 
by the mature spermatic mass while yet contained within the gonophore. 
This appearance, which is very common in the mature male gonophores of 
the Hydroida, suggests to us the idea that the corpuscles composing the mass 
are confined in an exceedingly fine tubular tissue. I have, however, in vain 
sought for any indubitable evidence of tubes, and I believe that the appearance 
in question is the result of a mere arrangement of the corpuscles—a condition 
induced in the plastic mass by the pressure exerted on it by the resisting walls 
of the gonophore as the mass within increases in volume ; for the component 
corpuscles have now become changed from the spherical form of the previous 
stage to a more oval form, and their axes are compelled by the surrounding 
pressure to take a definite direction. It is a phenomenon which in this view 
would be purely physical, and which we cannot avoid comparing to that of 
slaty cleavage, though occurring in an organized and living mass. 
Origin of the Generative Elements——Throughout the whole of the Hy- 
propa the generative elements originate between the endoderm and ecto- 
derm, and, with one exceptional condition to be presently described, are 
always formed in the walls of an organ strictly homologous with the manu- 
brium of a gymnophthalmic medusa. 
This organ forms the axile diverticulum in the young adelocodonie gono- 
phore, and the manubrium of the sexual medusa while it is represented by 
the sexual zooid which buds from the radiating canals in the gonoblastocheme 
or non-sexual medusa. 
