48o 



PATTEN AND HAZEN. 



[Vol. XVI. 



plate is a noncellular membrane forming the boundary of 

 the yolk. On the median side of the center of the plate is 

 a shallow outfolding (PL XXVI, Fig. 56, ejid) that marks the 

 beginning of the tubular portion of the duct. 



In the next stage 'this outgrowth (PL XXVII, Figs. 59-64) 

 has formed a short tube, with its solid distal end growing 

 towards the median line and meeting the ectoderm at the base 

 of the fifth leg ; the margins of the original plate now form the 

 funnel-shaped opening (nephrostom }) into the underlying space. 



Fig. 2. — Diagrams representing two stages in the development of the nephridial lobes and the 

 duct. They represent the left halves of the nephridia seen from the neural side. Clusters 

 of the nephridial cells are seen in the chelicera, the 2d, 3d, and 4th legs. The end sac and 

 nephridial duct are in the 5th leg. At this time the nephridial cells are large and granular. 

 The end sac is a closed cavity with a few granular nephridial cells appearing on its ventral 

 surface . 



The lips of the funnel have gradually united with the membrane 

 over the yolk, and at the same time nuclei migrate into the mem- 

 brane. Thus, a closed sac is formed which we have called the end 

 sac. The entire ventral wall is formed by the nephric plate, which 

 represents the somatic layer of the fifth somite. The end sac 

 apparently represents the coelomic cavity of that somite, and the 

 dorsal wall is formed from the splanchnic layer of the somite. 



