ON THE CCELOM. GENITAL DUCTS, AND NEPHEIDIA. 491 



Vejdovsky considers it probable that they are derived from the 

 epiblast, a conclusion which agrees with the known develop- 

 ment of the posterior nephridia. 



The mesoblast in the Oligochsetes is formed, as in all 

 Annelids, as two germ bands, which become broken up into 

 separate somites. The hollowing out of these gives rise to tlie 

 coelomic follicles, which increase in size, surround the gut (a 

 stage resembling what we find in the Nemertines), and fuse 

 below it (figs. 6 and 25). The transverse septa, between 

 adjacent follicles, become pierced, allowing a communication 

 from one to the other (Kowalevsky, 68; Hatschek,48; Wilson, 

 109; Vejdovsky, 101). From the wall of certain of these 

 follicles the gonads are developed, whilst others remain sterile. 

 The number and position of the fertile follicles varies consider- 

 ably according to the family of the worm in question, and even 

 amongst difi'erent individuals of the same species (Woodward 

 observed an earthworm with seven pairs of ovaries; 113, 114). 



The genital ducts (peritoneal funnels) develop as a thicken- 

 ing of the coelomic epithelium in the fertile segments, which 

 grows outwards towards the epidermis, with which it fuses 

 (figs.6,7,and25). Vejdovsky, who has followed thedevelopment 

 of these organs in several forms, such as Stylaria, Chsetogaster, 

 the Enchytrceids, and Tubificids, says: "Die Anlage des 

 Samenleiters wiederholt sich nach dem oben Dargestellten in 

 iibereinstimmender weise bei alien bisher beoachtete Familien. 

 Die zuerst zum Vorschein kommende Anlage des Samentrichters 

 besteht aus einer Zellvermehrung des Peritoneums an den 

 Dissepimenten der betreffenden Segemente^' (100). His 

 observations have been confirmed by Bergh (8) and Lehmann 

 (74) in the Lumbricids.i In the case of the male ducts, these 

 organs may be further complicated by the fusion of two con- 



1 Beddard (4) tried to show that the genital ducts were derived from the 

 nephridia in Acanthodrilus. The few facts he brings forward from the very 

 scanty material at his disposal do not, I think, prove his case. The theory 

 of Claparede that the genital ducts of the Oligochtetes were the modified 

 nephridia of the genital segments was founded on an erroneous notion, 

 since thoroughly disproved by Vejdovsky's observations. 



