Artificial Parthenogenesis in Thalasserna Melhta 129 



embryos is clear from an examination of Figs. 41 and 43 (cells 

 designated at oes) which should be compared with Torrey's Figs. 

 loD and 6B, respectively. 



The enteric cavity becomes secondarily divided into stomach 

 and intestine by a partition, consisting of a double row of cells, 

 which grows across from the dorsal wall and completely divides 

 the stomach from the intestine except on the ventral side where 

 an .opening persists. The division of the archenteron into two 

 cavities by this septum is well shown in Fig. 44, although the sec- 

 tion is a horizontal one and does not show the oesophagus and 

 the communication between the stomach and the intestine. The 

 ectodermal oesophagus secondarily acquires an opening into the 

 stomach, but the anus, which is not formed until a very late stage 

 in the normal development, has never been observed in the par- 

 thenogenetic larvae. 



Fig. 44 is drawn from a CO2 trochophore, which was killed 31 

 hours after the eggs had been treated with carbonated water. 

 Although larvae were raised for a considerably longer time than 

 this, differentiation rarely proceeded beyond the condition indi- 

 cated in the preceding figure. In the trochophore here repre- 

 sented, in addition to the digestive tract which is differentiated 

 into mouth, oesophagus, stomach and intestine, the prototroch 

 is present, and the high columnar cells bearing the apical flagella 

 are distinctly shown. A few cells of the larval mesenchyme 

 (ectomesoblast), stippled in this and the two preceding figures, are 

 seen scattered between the body wall and gut, to both of which 

 they are adhering. 



I have not observed the definite ventral neural ciliated region 

 described by Torrey, but occasionally more or less irregular patches 

 of cilia have been found in this portion of the larva, as they have 

 been, in fact, in other regions as well. 



5 Rudimentary Cells 



The remarkable rudimentary cells whose origin and fate Torrey 

 has so accurately described in Thalassema, are also recognized in 

 the parthenogenetic embryos, although I hardly think they are 

 as numerous here as in embryos raised from fertilized eggs. These 



