78 KARM NARAYAN BAHL 



one of the cells of this group is larger than the rest (fig. 14b), 

 and we can infer that this large cell is the so-called ' funnel- 

 cell '. It would seem, therefore, that this large cell, as it 

 pushes itself into the septum, is the forecast of the whole 

 nephridium, and is a ' funnel-cell ' in the sense in which 

 Bergh uses it. And later this large cell divides and gives off 

 cells smaller in size than itself ; and wliile these smaller cells 

 go to form the body of the nephridium the large cell develops 

 into the funnel and becomes a ' funnel-cell ' in the sense in 

 which Staff uses it. 



7. Development of the Secondary Nephridia, Septal 



AND Integumentary. 



At the end of the second stage of nephridial development, 

 as we have seen, a typical segment of the embryo contains two 

 pairs of nephridia — an integumentary and a septal. Soon 

 after, rudiments of other nephridia, both septal and integu- 

 mentary, begin to appear. These rudiments of secondary 

 nephridia (all nephridia appearing after the first pair, septal 

 and integumentary, have been grouped together under the 

 term ' secondary ') can be seen both in sections and in whole 

 preparations of embryos of suitable age as deeply-staining 

 masses of cells on the septa and the body-wall. In order to 

 study the development of these secondary nephridia, two 

 sets of embryos should be selected— the first set, consisting of 

 those embryos which are fully formed and are about to hatch 

 out of their cocoons : these show the secondary nephridia at 

 a fair degree of development ; the second set, consisting of 

 those embryos which are not fully formed and would take some 

 time before they are ready to hatch out : these show secondary 

 nephridia in their very early rudimentary condition. It may be 

 difficult, in the beginning, to distinguish embryos belonging 

 to these two sets, but when one gets familiar vnth. them after 

 opening a number of cocoons, one can always distinguish 

 them with a fair degree of accuracy. A surer method of distin- 

 guishing the embryos of two sets externally is to examine the 

 setal line. In fully-formed embryos the circlets of setae are 



