hall: MESOJ^ErHROS AND MULLERIAN DUCT IN AMPHIBIA. 79 



glomerular cavity, that portion of it which lies at the mouth of the first 

 neplirostome becomes pai'tially cut off to form Vv'hat I shall call the 

 " nephrostomal cavity" (Fig. 39, cav. n]jh''stm.). Whether this small 

 cavity has any ontogenetic or phylogenetic significance, I do not know. 

 It becomes more and more completely cut off in later stages, only to 

 disappear entirely at a still later stage. The first nephrostome opens 

 into the nephrostomal cavity four sections anterior to the point marked 

 cav. n])Wstin. in Figure 39. In the veutro '.ateral angle of the nephro- 

 stomal cavity may be seen the thickened band already described for 

 previous stages. It runs caudad and, just behind the point where the 

 nephrostomal and glomerular cavities become confluent, passes out on 

 to the shelf (Fig. 38, tae. eHh. a). Here it is joined by a similar band 

 from the second nephrostome {tae. e'th. /?). The section figured cuts 

 this baud just anterior to the point where it passes out to join the 

 anterior band. The shelf extends much farther back than formerly 

 (16 sections posterior to the 2nd nephrostome). The thickened band 

 runs downward around its posterior edge and then furwai'd along its 

 ventral surface, — that is, along the dorsal wall of the sub-glomerular 

 cavity. The extent and position of the band are represented in Figure J, 

 p. 88. 



In another larva, otherwise like the one last described, there is a 

 slight accentuation of the thickening of the lower lip of the second 

 neplirostome, similar to, but smaller than that of the next stage, which is 

 shown in Figure 40 (Plate 4). In neither of the larvae just described, 

 however, has the thickened disk of the first nephrostome appeared, 

 although it was present in Larva III. 



Larva V, Ifl mm. 



In this larva the local tliickenings near the first and second nephro- 

 stonies have both become quite pronounced (Fig. 41, evg. 1, and Fig. 40, 

 evg. 2). The anterior one (Fig. 41) is not dii-ectly ventral to the first 

 nephrostome, but lies behind it, for the nephrostome opens into the 

 dorso-lateral angle of the nephrostomal cavity {cav. nph'stm.) eight sec- 

 tions anterior to the one figured. The nephrostomal cavity extends 

 farther caudad than in previous larvae and its anterior end lias 

 become so narrow that it forms a postero-ventral continuation of the 

 nephrostome, so that it is difficult to discern where the one ends and 

 tlie other begins. At tae. e'th. a (Fig. 40) the band from the first 

 nephrostome is shown. 



