216 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



The ectodermal stomodaeum and proctodaeum are formed in the usual 

 way in the roach. From the lateroventral angles of these invaginations 

 cellular ribbons arise, two from the stomodaeum growing backward, two 

 from the proctodaeum growing forward until they meet, their outer 

 surface in contact with the splanchnic mesoderm. The ribbons then 

 widen and fuse, first, along the lower and then along the upper, median 

 longitudinal line, forming the tubular mid-gut epithelium. The muscles 

 of the mid-gut are derived from the splanchnic mesoderm. Embryolo- 

 gists are for the most part in agreement as to this process, but there is a 

 distinct difference of opinion concerning to which germ layer these 

 epithelial ribbons owe their origin. Wheeler (1889) states "that it is next 

 to impossible to come to any definite conclusion as to the mode of origin 

 of the entoderm in Blatta.'' Heymons (1891, 1895) maintains that the 

 ribbons arise from the ectodermal cells of the blind ends of the stomodaeal 

 and proctodaeal invaginations. More recently Nusbaum and Fulinski 

 (1906) in an elaborate study on this question conclude that the cells that 

 give rise to the epithelial ribbons are not a part of the ectodermal invagina- 

 tions but have arisen from bipolar entodermal rudiments upon which the 

 blind ends of the invaginations impinge but from which they are entirely 

 independent. This subject is discussed in more detail in Chap. VI of 

 this text. 



With the absorption of amnion and serosa and the dorsal closure of 

 both of the body wall and of the mid-gut, the embryo completes its 

 development, the young making their escape about three weeks after the 

 ootheca first appears at the vaginal opening. 



Since the development of the brain, ventral nerve cord, visceral 

 system, sense organs, integument, stomodaeum, proctodaeum, and other 

 ectodermal derivatives in the roach closely resembles that described in this 

 text for other Orthoptera, there is no need for repetition. 



The accounts of Wheeler (1889), Cholodkowsky (1891), and Heymons 

 (1895) on the development of Blattella germanica differ somewhat on minor 

 points. 



ISOPTERA 



The Termite (Eutermes rippertii ?) 



The unsegmented egg, as described by Knower (1900), is oval, about 

 0.5 mm. long by 0.22 mm. in diameter, enlarged at the posterior (micro- 

 pylar) end and markedly convex on the ventral side. As here considered, 

 the micropylar end is the definitive as well as the primary posterior pole, 

 and the convex side becomes the final ventral surface. Polar bodies 

 appear at about the middle point of the flattened dorsal surface of the 

 yolk mass. The pronucleus returns from the dorsal side to the middle 

 of the yolk where division takes place. The cleavage nuclei after repeated 



