326 
NOTES. 
testicles formed by numerous canals twisted around one another : they were 
much developed and placed along-side the ovaries, which they equalled in num- 
ber.” Their real nature was ascertained by the detection of spermatic animal- 
cules in them ; and these were also found in the Act. effceta Ann. des Sc. 
Nat. tom. viii. p. 283, &c. 
3. Structure of the Hydra. Page 99. 
Augustus Josephus Corda has recently published a memoir on the anatomy of 
Hydra fusca, where he shews that this is greatly more complicated and curious 
than has hitherto been imagined. According to Corda each tentaculum forms a 
slender membranaceous tube filled with an albuminous nearly fluid substance 
intermixed with some oleaginous particles this substance swells out, at certain 
definite places, into denser wart-like nodules which are arranged in a spiral line. 
These are the tubercles noticed by all observers, but no one had hitherto develop- 
ed their structure. Corda says that each nodule is furnished with several spini- 
gerous vesicles used as organs of touch, and with a very singularly constructed 
organ for catching the prey. The organ of touch consists of a fine sac enclosing 
another with thicker parietes, and within this there is a small cavity. From the 
point where the two sacs coalesce above, there projects a long cilium or capil- 
lary spine which is non-retractile, and apparently immoveable. Surrounded by 
these cilia, and in the centre of the nodule , is placed the captor organ, called the 
hasta. This consists of an obovate transparent sac, immersed in the nodule, 
with a small aperture even with the surface. At the bottom of the sac, and 
within it, there is a saucer-like vesicle, on whose upper depressed surface is seat- 
ed a solid ovate corpuscle that gives origin to, or terminates in, a calcareous 
sharp sagitta or arrow, that can be pushed out at pleasure, or withdrawn till its 
point is brought within the sac. When the Hydra wishes to seize an animal, the 
sagittce are protruded, by which means the surface of the tentacula are roughen- 
ed, and the prey more easily retained : and Corda believes that a poison is at the 
same time injected, which will explain the remarkable fact of the almost instant 
death of the prey. 
The nodules of the tentacula are connected together by means of four muscu- 
lar fibres or bands which run up forming lozenge-shaped spaces by their inter- 
sections. These are the extensor muscles of the tentaculum. They are again 
joined together by transverse fibres, which Corda believes to be adductor mus- 
cles, and to have also the power of shortening the tentacula. Corda states that 
there is no communication between the tube of the tentaculum and the cavity of 
the body. 
The lip of the mouth is armed with hastce and cilia similar to those of the 
tentacula, but the rest of the body is destitute of them. 
The skin consists of two strata, the exterior largely cellular, the inner with 
cells of a much smaller size. In the latter the gemmules lie. Under it there 
is a layer consisting of densely aggregated cells, filled and coloured with minute 
granules. This layer Corda regards as muscular ; and within it there is another 
layer which, from its texture and position, he says may be called the villous coat. 
From the inner surface of this, numerous villi project into the stomachal cavity, 
collected into masses which are divided from each other by passages destitute of 
villi. Each of the villi is in the form of a cylindro-conical pellucid vesicle filled 
with the nutrient matter ; and most of them are perforated on the tip while 
3 
