960 MR. H. B. MEHRA ON TWO NEW INDIAN 



the septum from which it is formed and consist of a thin layer of 

 muscle fibres covered both on the inner and outer sides by a 

 peritoneal layer of thin flattened cells. It is filled with sperms 

 in various stages of development, and is in appearance and struc- 

 ture similar to the sperm-sac in the Naididse. 



A large portion of the body-cavity in the 6th segment is 

 separated off laterally and ventrally from the smaller peripheral 

 portion, contains all the organs belonging to the segment, and is 

 tilled with a huge mass of developing sperms. This pai-t is sur- 

 rounded by a wall, which is continued dorsally into the body-wall, 

 its side walls become continuous ventrally to form the ventral 

 portion of the wall, except at the ventro -lateral corners where 

 the spermathecal ducts interrupt it as they pass out to their 

 openings, and in the transverse sections of the worm here the 

 peripheral chamber is thus divided up into a median ventral 

 and two lateral parts (PI. II. figs. 8 & 9). The wall which so 

 separates the two portions of the body-cavity in the segment 

 is composed of modified peritoneal layers, with a layer of 

 circular muscle fibres in between. The outer peritoneal layer 

 consists of branched cells of an irregular outline, the fibrillar 

 branches given off from the various cells anastomose forming 

 a sort of loose network, which with fairly big spaces enclosed 

 in between gives the whole layer the appearance of paren- 

 chyma and is about five times as thick as the rest of the wall 

 (PI. III. fig. 10). The middle layer, consisting of circular 

 muscle fibres, becomes continuous with the same layer of the 

 ventral body-wall at the openings of the spermathecal ducts. 

 The inner layer consists of cells fairly regularly arranged and not 

 of the same breadth throughovit, less regular on the lateral 

 portions of the wall. This layer is continued dorsally into the 

 peritoneal layer of the body-wall, which also in this segment may 

 be parencliymatoas in character, hence sometimes the whole 

 peritoneal cavity, i. e. the space outside the wall of the central 

 chamber, is tilled with parenchymatous tissue formed by these 

 peritoneal layers. The wall of the central chamber in the front and 

 hinder parts of the segment gradually comes near the body- wall, 

 and consequently the peripheral cavity becomes much more 

 reduced ; posteriorly it completely joins the body-wall about the 

 level of the ventral setae, in front of the seminal funnel ; 

 anteriorly it unites with the body-wall near septum 5/6, of which 

 it appears to be a backward continuation, for in structure like 

 the septum it is composed of three layers, the outer and inner 

 peritoneal ones of more or less parenchymatous character with 

 the middle one of muscle fibres. It seems clear that a good deal 

 of support is afforded to the spermathecal ducts and proper 

 protection to the developing sperms by this arrangement. 



The anterior sperm-sac described in many Tubificids is here 

 absent. The ovisac is formed as a pouch by the extension back- 

 wards of septum 7/8 and lies in segment 8, extending behind nearly 

 to septum 8/9. It surrounds a part of the sperm-sac and extends 



