i9o8.] 



J. Stephenson: The Anatomy of some Aquatic Oligochœta. 



261 



pressure it may be extruded whole from the body of the worm. When teased, it is 

 found to consist entirely of oval particles, each homogeneous and non-nucleated, 

 bright and highly refractile, in diameter a third or a quarter the size of a lymph- 

 corpuscle of the animal's body-cavity. Singly these particles are transparent ; in 

 the aggregate, in the body of the animal, they are opaque, and the mass which they 

 compose is under the microscope by transmitted light quite dark. The similarity 

 of the particles to those included in the corpuscles of the body-cavity has been 

 mentioned ; it may be added that appearances would seem to suggest that certain of 

 the body-cavity corpuscles are mere aggregates of such particles. 



It may be conjectured that the great swelling of the body in segments v and 

 vi of the specimen represented in fig. 21 is due mainly to the growth of the opaque 

 body, and the consequent pushing forwards of the dilated seminal vesicles, which 

 formerly stretched, backwards as far as the hinder end of the ninth segment. 



The genital setœ (tes:t-fig. 3) are the modified ventral setae of the sixth segment, 

 and replace the setae of ordinary type in animals with sexual organs in an advanced 

 state of development. They are 09 mm. or less in length, stout in build, curved 



Pig. 3. — Genital setae of Nais variabilis , var. punjahcnsis. 



and somewhat swollen near the free end, which may or may not be bifid. If bifid, 

 the prongs of the fork are short, blunt, and approximately equal in length ; if not, 

 the extremity is blunt and rounded. There may be two setae in each bundle, or 

 sometimes three, one at least in either case being bifid, the other frequently with a 

 single point. 



I cannot find any reference to a white mass of similar constitution to the one 

 described above. Michaelsen [4] figures and describes only ova in the ovisac of A^. 

 elinguis; Piguet [7] figures something similar for Pristina longiseta, and describes the 

 ovisac of N. communis, but again speaks only of ovarian cells and ova. The 

 ordinary works of reference do not contain any allusion to a white mass of the 

 nature of the above. It is always stated that "albumen" is found within the 

 cocoons of Oligochaeta, but its source is not mentioned ; it seems possible that we 

 have here an indication of its origin. {Cf. also Pristina, post.) 



