494 MAYOR. 



haematoxylin and congo red. The sections deviate very slightly 

 from the transverse, the right dorsal side of the oral end of the larva 

 being cut first. As the oral end was cut first the right side of the larva 

 is to the right in the preparation. The sections are 7 )U in thickness 

 and there are 57 of them in all. As in the previous larva, the aboral 

 end is somewhat flattened. 



The oesophagus is circular in cross section, and extends on the 

 ventral side through one more section than on the dorsal side. On the 

 ventral side it extends into section 22. After leaving their junction 

 with the oesophagus in section 22 the mesenterial filaments of the 

 first and second mesenteries of either side are not fused as in larva A. 

 Those of the first pair of mesenteries extend on either side into section 

 42 and those of the second pair are turned from the aboral end of the 

 oesophagus outwards toward the oral end of the larva extending on the 

 right into section 12 and on the left into section 17. The filaments 

 of the first pair of mesenteries are enlarged on the right side between 

 sections 30 and 37, and on the left side between sections 37 and 39, 

 those of the second pair of mesenteries decrease gradually in size 

 until they end. Only mesenteries / and // are complete. 



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

 ing table, which shows the number of the section where each mesentery 

 begins and ends: 



Number of mesentery 1 II III IV V VI 



Right side of larvae 



Oral end section No 



Aboral end section No. 

 Left side of larvae 



Oral end section No. 



Aboral end section No. 



Although traces of the fifth pair of mesenteries extend into section 

 44 these mesenteries are only slightly developed in the aboral half of 

 the larva. 



Group II. Larva C. 



This larva is in about the same stage of development as larva B, 

 but the fifth and sixth pairs of mesenteries show more clearly. It 

 was fixed in a saturated solution of corrosive sublimate plus 1% 

 acetic acid. The 90 sections were stained with Heidenhain's iron 

 haematoxylin and congo red, each being 5 /x thick. The aboral end 



