ON TWO NEW GENERA OF AQUATIC OLIGOCH^TA. 305 



Fig. 30. Phreodrilus subterraneus, longitudinal section through atrium at region lettered a in fig. 7, to show 



commencement of periatrial sac. sp, space, filled with spermatozoa, pro- 

 duced by the splitting off of the muscular coat of the atrium. 



Fig. 31. „ „ egg-sac containing developing ova. s, walls of sac, which are simply formed 



by a pushing back of the septum ; o, clumps of developing ova. 



Fig. 32. „ „ periatrial space containing spermatozoa and nuclei. 



Fig. 33. „ „ muscular wall of periatrial space in transverse section. 



Plate III. 



Phreodrilus subterraneus, chief vascular trunks in four of the anterior segments, d, dorsal vessel ; 

 h, hearts ; bgl, blood-gland ; v, ventral vessel ; si, supra-intestinal ; n, network upon oesophagus. 

 Pelodrilus violaceus, dissection showing apertures of vasa deferentia of one side, opening by separate 

 pores, 6 1 , 6 2 . s, setae. 

 „ „ section through commencement of oesophagus to show septal glands (sg), and 



their ducts (d) ; bl, dorsal blood-vessel ; sp, septum. 

 Phreodrilus subterraneus, developing ova at different stages. 



Pelodrilus violaceus, interior of portion of sperm sac to show the coiling of the vas deferens (v.d) 

 within the sac ; bundles of developing spermatozoa (sp) are also shown ; 

 sps, wall of sperm -sac. 

 Fig. 39. „ „ dissection to show vasa deferentia and oviduct. /, funnels of vasa deferentia ; 



$ , external orifices ; spt, septum ; od, oviduct ; s, setse. 

 Fig. 40. „ „ oviduct in longitudinal section. 



Fig. 41. „ „ a, ovary ; b, nearly mature ovum ; c, fully mature ovum. 



Fig. 



34 



Fig. 



35 



Fig. 



3G 



Fig. 



37 



Fig. 



38 



VOL. XXXVI. PART II. (NO. 11). 2 Z 



