168 



ON A NEW ORGAN IN AN EARTHWORM. [Jime 17, 



extension of the peritoneum with lining of cells and a few slender 

 muscular fibres. The wide opening at either end is conspicuous, 

 and there is no difference of structure at this orifice. The wall 

 simply leaves off. Transverse sections (text-fig. 39) taken at the 

 widest part of the sac show that it forms here an absolutely 

 closed sac, a chamber distinct from the genei-al ccelomic cavity. 

 Corpuscles were floating about, and, as already mentioned, 

 nephridial tufts are frequent in the interior. Whatever may be 



Text-fig. 39. 



Longitudinal section through bodj'-wall and underij'ing ccelomic pouch of 

 Fheretima posthuma. 



1, nepliridia ; other letters as in text-fi^ 



,38. 



the natui'e of this seiies of separate ccelomic cavities, there is in 

 one genus of OHgochseta a set of cavities which may perhaps be 

 comparable to them. In Lyhiodrilus^ the area surrounding the 

 lateral setse is in a similar way shut off fi'om the general ccelomic 

 cavity. There is not, howevei', in this case any conspicuous 

 ojDening of the cavity so formed into the genei-al cavity of the 

 segments ; the cavities in question ai-e completely separated. 

 Possibly in both cases we have to do merely with that tendency 

 to the division of the ccelom into a number of completely or 

 incompletely separated chambers which is so general in ccelomate 

 animals. In any case, the facts described in the present com- 

 munication appear to be novel, and at least fui'nish another 

 example of the commencing subdivision of the ccelom in the 

 Oligochseta which culminates in their nearest allies the Leeches. 



1 Beddard : " On the Structure of an Earthworm allied to Nemeriodrihis, &c.," 

 Quart. Journ. Micr. Sci. xsxii. p. 546. 



