496 MAYOR. 



The mesenterial filaments of the first and second pairs of mesen- 

 teries of the right side are not fused together after they leave the 

 oesophagus. The first of these extends from sections 13 to 26, the 

 second from sections 13 to 25. On the left side the filaments are fused 

 from their junction with the oesophagus at section 13 as far as section 

 17, below which the filament of the first mesentery extends to section 

 29, that of the second to section 25. The filaments of the mesenteries 

 are enlarged as follows: those of the first pair on the right between 

 sections 19 and 22, on the left between sections 18 and 23, those of the 

 second pair on the right between sections 19 and 23, on the left between 

 sections 18 and 21. 



The length and position of the mesenteries is shown in the following 

 table : 



Number of mesentery / // III IV V VI 



Right side of larva 



Oral end section No. 



Aboral end section No. 

 Left side of larva 



Oral end section No. 



Aboral end section No. 



Only mesenteries /, // and /// are complete. 



Group II. Larva E. 



This larva was fixed and stained like larva D. The aboral end was 

 cut first and the sections are so nearly transverse that all sides of the 

 circular oesophagus appear in the next to the last section of the series. 

 There are 55 sections, each 7 ^t thick and they are numbered from the 

 oral end. 



The oesophagus is elliptical in cross section. Its dorsal side ends 

 at section 7 and its ventral side at section 11. 



The mesenterial filaments of the first and second pairs of mesen- 

 teries are separate where they leave the oesophagus. The filaments 

 of the first pair extend on either side from the oesophagus, at section 11, 

 to section 47. Those of the second pair extend on the right to section 

 31 and on the left to section 35. The filaments of the first pair are 

 enlarged in cross section on both sides between sections 23 and 44. 

 Those of the second pair on the right between sections 16 and 29 and 

 on the left between sections 16 and 34. 



The position and extent of the mesenteries is shown in the following 

 table: 



