40 
of their body after the manner of a leech, and they are sensible to the presence of 
light, which they always approach." — {Rymer Jones). 
The wall of the body is composed of two distinct layers of a kind of sarcode, 
the "ectoderm," or outer wall, and the "endoderm," or inner 3 it would appear 
as if there was but little differentiation between them, for it has been proved from 
actual experiment, by turning a polype inside out, the relative position of the 
ectoderm and endoderm being reversed, that each will perform the function of the 
other. 
Dr. Carpenter's description ("Microscope and its Revelations," 3rd 
edition, pp. 543, 544) of the " urticating organs " covering the tentacula 
was here quoted. 
The reproduction of the Hydra was then described, the facility with 
which artificially detached portions of a polype developed into complete 
individuals being noticed, as well as the gemmation, or budding process, 
which took place most freely in the neighbourhood of the digestive cavity, 
and then only under the conditions of warmth and a plentiful supply of 
food. The continuance of the species during the cold of winter was pro- 
vided for by a true reproductive process, or act of generation, which was 
thus described : — 
At certain times of the year two sets of cells are developed in the walls of the 
body, one set at the base of the tentacles, these being the " spermatic capsules," 
and the other nearer to the base or foot, forming the "ovigerian capsule," which 
contains in Hydra viridis only a single ovum, but in H. fusca as many as six or 
seven ova. 
It would appear that occasionally instances occur in which " spermatic capsules ' ? 
only are developed on one animal, the " ovigerian capsule " being developed sepa- 
rately on another, but the more general rule is, that both are produced on the 
same polype. By the simultaneous rupture of these cells, the spermatozoids of 
the spermatic capsule find their way to, and fertilize the ovum, which is seemingly 
exposed to their influence by a thinning-away of the external membrane. 
The ova covered with a horny substance possess a great power of resistance to 
the cold, thus preserving their vitality until the return of conditions favorable for 
their existence, when development begins to take place. This proceeds up to a 
certain point, the covering of the ovum bursting, liberates the embryo, which 
becomes ciliated, and for some time swims freely in the water ; in this condition it 
is known as a " gemmule." Gradually it becomes elongated, and by one end 
which tapers away it attaches itself to some solid body, then the development 
into the polype form quickly takes place. At the unattached end the germinal 
membrane thins away ; ultimately an aperture exists which becomes the mouth, 
and around it the tentaoles or arms soon make their appearance. 
Mr. W. W. Stoddart mentioned that H. fusca was to be found in 
Malago Brook, Bedminster, and H. viridis in ponds on Durdham Down, 
lie found the best way of mounting them for the microscope with their 
