677 



(»Bursa copulatrix« Perrier). This latter I regard as the equi- 

 valent of the «penis sheath« of the Tubificidae. The muscular 

 penis evidently corresponds to the penis in the Tubificidae, while the 

 muscular tube leading to it is the homologue of the muscular region 

 of the atrium in these and other »Limicolae«. Vejdovsky has rightly 

 pointed out that the glandular part corresponds to the »vesicula semi- 

 nalis« which is sometimes (e. g. in Psammoryctes) sharply marked off 

 from the non-glandular region of the atrium. The condition which 

 characterizes Pontodi-ilus can be derived from Eudrilus on the suppo- 

 sition that the vas deferens, which in Eudrilus opens some way down 

 the vesicula and not at its apex, has moved still further down, so that 

 the vesicula comes to be a diverticulum, opening in common with the 

 vas deferens into the muscular atrium. In TypJiocus^ I am able to 

 record here for the first time, the vesicula and vas deferens are still 

 further divorced ; they penetrate the body wall independently and only 

 unite just beneath the epidermis. This latter fact is to a certain extent 

 confirmatory ofVejdovsky's opinion* that a long sac like structure 

 in Ocnerodrilus, which opens in common with the vas deferens, is really 

 the atrium. 



The identity of structure between the glandular bodies appended 

 to the termination of the vas deferens in Eudrilus, Typliocus etc. leads 

 to the inference that they are homologous, while the relations of the 

 vas deferens to this body in Eudrilus clearly favours the supposition 

 that it corresponds to the atrium in the »Limicolae«. The so called 

 »prostate« of Perichaeta undoubtedly present certain ressemblances to 

 the prostates of many Limicolae e. g. Tubificidae; it consists of groups of 

 glandular cells, each cell furnished with a long prolongation, attached 

 to a series of branching ductules which unite and open into a muscular 

 atrium. In the Limicolae however and in Moniligaster^ the prostates 

 are formed by a metamorphosis of certain peritoneal cells. \\\ Peri- 

 chaeta the supposed prostate is covered by a continuous 

 layer of peritoneal cells; this disproves any homology between 

 the prostates ^^î Perichaeta and those of the »Limicolae«; it is this 

 peritoneal covering of the so called »prostate« in Peri- 

 chaeta which is the real homologue of the prostate of 

 Monilig aster and the lower Oligochaeta. A poj'itoneal layer 

 also covers the atrium of Eudrilus^ Acantliodrilus etc. but is nowhere 

 modified to form a prostate. The structure of the gland in question in 

 Perichaeta only differs from the atrium of Acanthodrilus in the fact that 



4 1. c. p. 144. Woodcut fig. IV. 

 ^ See last paper. 



