DEVELOPMENT OF AGAKICIA. 499 



Group III. Larva G. 



The chief difJerences between this larva and larva F pertain to the 

 form of the oesophagus and gastrovaseular cavity. It was fixed in 

 Flemming's fluid and stained with Heidenhain's iron haematoxyhn. 

 The series consists of 154 transverse sections each 7 /jl thick. The 

 aboral end was cut first, so that the sections are viewed from this end, 

 but the numbering of the sections is from the oral end. 



The oesophagus is well invaginated and is circular or slightly oval 

 in cross section (Fig. 3, ^) as far as section 20. It is then interrupted 

 on the dorsal side, as seen in sections 21-23 (Fig. 3, B), after which 

 the ectoderm becomes divided also on the ventral side. The slight 

 deviation of the sections from the true transverse plane is such that 

 their ventral edges are more aboral than their dorsal edges, a fact 

 which can be learned from the table showing the extent of the mesen- 



FiGURE 3. Agariciafragilis. Larva G. Transverse sections, aboral aspect. 

 Ectoderm and mesoglea colored black. A, section 19; B, section 23. X 90. 



teries, and from the fact that the last few sections cut the ventral 

 side only of the larva. There can be no doubt, therefore, that the 

 oesophagus is interrupted on the dorsal before it is on the ventral side. 

 There are only two pairs of mesenterial filaments, those of the first 

 and second pairs of mesenteries. The filaments of the first and second 

 mesenteries are fused on the left from sections 24 to 31 and on the right 

 from sections 24 to 33. The sections of the filaments of the first pair 

 of mesenteries decrease in size until section 57 is reached, after which 

 they increase in size on both sides up to about section 124, where 

 they are somewhat larger than those of the second pair of mesenteries. 

 After this they decrease in size till they end, on the right at section 135 

 and on the left at section 132. The filaments of the second pair of 

 mesenteries increase in size up to about section 57. In section 40 

 they have about the same size as those of the first pair of mesenteries 



