304 Mr. J. S. Bowerbank on the Cocoon of a Leech. 



coon of that species in this manner. When the animal is about 

 to produce one of these bodies, it is observed to be greatly con- 

 tracted both above and below the uterus, a distension then takes 

 place between these constrictions, and a surrounding membranous 

 structure is thrown off which becomes of a milky white colour ; 

 into this the animal forces with some effort the whole contents 

 of the uterus. This done, it elongates the anterior portion of 

 the body, and withdraws its head as from a collar. After the 

 animal has firmly fixed it to some substance, it fashions it with its 

 mouth until it presents an oval form. 



This description enables us in some measure to account for the 

 mammseform appendages of the horny case of the species under 

 consideration, and which differs somewhat in the structure of 

 these parts from all the cocoons described by Dr. Johnson, in 

 which, instead of the protuberant mammse, we find simply cir- 

 cular orifices ; but it does not in any shape enlighten us upon the 

 mode of the construction of the extraordinary and complex spon- 

 geous tissue which surrounds our species of cocoon. 



The mammseform ends of the cocoon are of an oval form, and 

 project in about an equal degree beyond the inner and outer sur- 

 faces previously to their becoming perforated, and the length of 

 the oval is somewhat increased by a considerable thickening of 

 the substance of the body immediately surrounding them. The 

 communication between the inner and outer surfaces appears to 

 be effected in a very singular manner. In one case where I made 

 a section of one of these organs at right angles to the natural 

 surfaces of the body, it appeared perfectly solid ; in another a 

 small cavity only existed near the inner surface of the case ; but 

 in a third specimen the appearance presented was of an exceed- 

 ingly singular description. The outer end of this organ had a 

 small irregular perforation which led into an ovoid cavity imme- 

 diately beneath, and the long axis of which was in a diagonal 

 direction as regards the axis of the body of the cocoon, and the 

 inner surface of this cavity appeared to be furnished with three 

 or four ribs, as represented by PI. XVIII. fig. 5» with a power 

 of 94 linear, and PI. XVIII. fig. 6. with a power of 160 linear. 

 Upon opening the cocoon I found that the opposite end of the 

 mamma had disappeared, and in lieu of solid substance there was 

 a large dome-shaped cavity, the top of which was separated from 

 the inner end of the ovoid cavity in the external end by a very 

 thin layer of horny structure ; and indeed at one spot there were 

 appearances as if a minute communication existed between them, 

 but from the oblique position of the ovoid cavity I could not de- 

 termine this with certainty. The other extremity of the cocoon 

 did not exhibit precisely the same appearances ; in this case the 

 entrance to the ovoid cavity was much larger on the outer surface, 



