88 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



delamination, and this process may continue even after a part of the 

 blastoderm has been converted into the ventral plate. Before the 

 splanchnic mesoderm has completely separated the yolk from the body 

 cavity on the ventral side, some yolk cells migrate into the body cavity 

 where they arrange themselves irregularly along the sides of the body 

 wall. At first the cells are arranged singly and indefinitely along the 

 outer wall of the body, but later, increasing in numbers, they become 

 arranged in distinct groups. These yolk cells (entoderm) are both more 

 distinct and more numerous in the posterior part of the yolk sac; the 

 epithelial lining of the stomach probably is formed first in the neighbor- 

 hood of the proctodaeum and then extends forward to the stomodaeum. 

 It is certain that the yolk cells (entoderm) do not form a continuous sac 

 until some time after the formation of the mesodermic musculation of the 

 yolk sac. 



LEPIDOPTERA 



Leaving out of account statements of the mid-gut epithelium deriva- 

 tion from the yolk cells in the Lepidoptera, recent researches seem to 

 indicate that the epithelium may arise from independent bipolar mesen- 

 teron rudiments, or it may apparently arise from cells that lie in the 

 blind tips of stomodaeum and proctodaeum. In Pieris Eastham (1927) 

 found that the entoderm is formed in anterior and posterior rudiments 

 which develop in the positions of future mouth and anus and therefore 

 belongs to type I of Nusbaum and Fulinki (1909). Sehl (1931) and 

 Drummond (1936) apparently found a similar condition in Ephestia 

 kuhniella, the entodermal rudiments each developing the usual pair of 

 ribbons, from which the mid-gut epithelium is produced. Bipolar ento- 

 derm rudiments have likewise been described for Catocala nuyta by 

 Hirschler (1906) and for the tusser moth ( Anther aea pernyi) by Saito 

 (1937). Schwangert (1904) working with Endromis and Zygaena found 

 an anterior mesenteron rudiment which developed similarly to that of 

 Pieris but owing to the complex flexures of the embryo did not find the 

 posterior counterpart. 



On the other hand, in Lasiocampa (Schwartze, 1899), Bomhyx mori 

 (Toyama, 1902), Diacrisia virginica (Johannsen, 1929), Diacrisia vir- 

 ginica, D. latipennis, Estigmene acraea, E. congrua, and Isia isabella 

 (Richards, 1932) the mid-gut epithelial ribbons develop from cells lying 

 in the blind ends of the stomodaeal and proctodaeal invaginations. 

 Johannsen (1929) interprets the cells from which the mid-gut originates 

 in Diacrisia as latent entoderm, or "dormant," cells in the terminology 

 of Nusbaum and Fulinski (1909) under type VII (see page 72 of text). 

 Schwartze and Toyama, following Heymons' interpretation, regard the 

 mid-gut epithehum in the moths studied by them as derivatives of the 



