326 NOTES. 



testicles formed by numerous canals twisted around one another : tbey 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 mth a very singularly constructed 

 organ for catching the prey. The organ of touch consists of a fine sac enclosing 

 another mth 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 cUia, and in the centre of the nodide, 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 sharp sagitta or arrow, that can be pushed out at pleasure, or withdrawn till its 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 

 sagittoE 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 ca\'ity 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 thje 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 



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