Tae MuicroscopicAL NeEws 
AND 
NORTHERN MICROSCOPIST. ' 
No. 34. OCTOBER. 1883, 
HYDRA: ITS ANATOMY AND: DEVELOPMENT. 
By J. W. DUNKERLEY. 
(Continued from page 245.) 
HE ordinary mode of reproduction is by gemmation. When a 
Hydra is receiving more nourishment than it needs, it increases 
by a system of buds. That is, diverticula are developed, and what 
at first are merely blind or hollow sacs, gradually elongate and be- 
come pear-shaped. At the free end, and around the outer edge, 
minute processes are developed, and grow into tentacles, in the 
centre of which a mouth appears. The bud, which is now a per- 
fect Hydra, sooner or later breaks away. If the parent is well 
nourished the bud will not only all the longer remain attached to 
it, but will itself begin to bud; and several children and grand- 
children may be seen at the same time upon the parent. But if 
the supply of food be withheld, and no tentacles have formed, the 
buds will decrease and finally disappear. But if tentacles have 
been formed, however small, the buds will break away and live. 
At certain seasons of the year reproduction also takes place by 
the formation of spermatozoa and ova. The spermatozoa are 
formed within the spermatic capsules. These arise as minute 
conical tubercles a little beneath the base of the tentacles and 
form the testes. Fig. 62. They vary in number from three to 
eight. The spermatozoa were first made out by Mr. Gulliver, F.R.S. 
The length of each spermatozoon is about ¢?55 of an inch, and 
are bodies consisting of a very small oval head, to which a very 
delicate filament is attached. They may frequently be seen in 
motion when ripe within the unruptured testis, and can be made 
out by a one-inch objective. They are liberated by the burst- 
ing of the sac. When free, the spermatozoa swim freely in the 
water, by means of their filaments, and eventually reaching the 
ovum, fertilizes it. The ovary is formed in the substance of 
VOL. Ill. 
