DEVELOPMENT OF AGARICIA. 495 



of the larva was cut first and on the dorsal side, so that the ventral 

 side of the oral end occurs in nine sections after the dorsal side has 

 ceased to appear. 



The oesophagus is almost round in cross section and is shorter on 

 the dorsal side than on the ventral side, the length of the dorsal side 

 being approximately 50 /x, while that of the ventral side is 170 /x. 



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

 teries are continuous with the ectoderm of the oesophagus. On the 

 right side they are fused in section 24 but below that separate, the 

 filament of the first mesentery extending into section 64, that of the 

 second into section 57. On the left side they are fused as far as section 

 45, below which the filament of the first mesentery extends as far as 

 section 63 ; the second mesentery has no separate mesenterial filament. 

 The filaments of the first pair of mesenteries are enlarged and crescent 

 shaped in cross section on the right between sections 43 and 61 and on 

 the left between sections 40 and 59. The filaments of the second pair 

 of mesenteries are not thus enlarged and are approximately uniform 

 in cross section throughout their length. 



The lengths and positions of the mesenteries are given in the fol- 

 lowing table: 



Number of mesentery / II 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 D. 



Larva D, which was in nearly the same stage of development as larvae 

 B and C, was fixed in a saturated solution of corrosive sublimate, and 

 the sections were stained in Mallory's phosphotungistic acid haema- 

 toxylin. The plane of sectioning deviated slightly from the trans- 

 verse, the first part of the larva cut being slightly dorsal to the middle 

 of the right side. The 47 sections are each 7 /x thick. 



The oesophagus is elliptical in cross section, the long axis being 

 dorso-ventral. 



