EMBRYOLOGY OF THALASSEMA MELLITA 213 



throughout its course bears a row of powerful, active ciha. 

 Conn considered it to be the Anlage of the ciliated groove or 

 the collateral intestine of the adult. Hatschek described the 

 same organ in the form of EcJiiurus that he studied ; as has also 

 Salensky i^J^y) in the Naples larva. The latter ascribed to it a 

 respiratory function. Without doubt in the larva of TJialassema 

 it functions merely as a conductor of food from the stomach to 

 the intestine. 



c. Alimentary Tract. — The wall of the oesophagus, which is 

 very thick, secretes a cuticle. In Eupomatiis both the oeso- 

 phagus and anal end of the intestine are lined in the same way. 

 Conn has described a glandular region in the stomach wall im- 

 mediately under the oesophagus, and there seems to be some 

 evidence, especially in sections of the younger trochophores, 

 that the cells here have such a function. It is equally prob- 

 able, however, that the swellings occurring at regular intervals 

 in the stomach-wall of older trochophores (Text-Fig. 8, A) may 

 be concerned in digestion. Each of these contains a clear re- 

 fractive drop and also a few pigment granules (Text-Fig. 8, C 

 and D). 



d. Mcsoblast. — A detailed description of the development of 

 the mesoblast is reserved for a separate section and only its dif- 

 ferentiation in the trochophore will be indicated here. The 

 coelomesoblast is present in the form of two bands, each con- 

 sisting of only five subequal cells. These are closely applied 

 to the body-wall and lie in the usual position on each side of 

 the neural row of ciha, but are more widely separated than in 

 many annelids. The mesenchyme, on the contrary, is present 

 in great abundance and has attained a considerable degree of 

 differentiation (Text-Fig. 9, A\ many of the cells having now 

 been converted into muscles. The latter vary somewhat in 

 number and position in different individuals, but there are cer- 

 tain typical ones which are always present. Two or three ex- 

 tend from the apical plate to the oesophagus. These, with sim- 

 ilar muscles along the median line, running from the apical 

 plate to the mouth, widen the cavity of the cesophagus and 

 permit the passage of the larger particles of food. A group of 



