572 TEXT-BOOK OF ENTOMOLOGY 



clearly ectodermal structures. We must, therefore, they add, leave to later 

 researches the question of the homology of these organs, also of their relations 

 to the similar glands of Peripatus. 



The urinary tubes. These excretory vessels arise as paired evagi- 

 nations of the hind intestine or proctodseum. They are ectodermal 



structures arising as lateral diverticula of 

 the intestinal cavity (Fig. 546). Figure 

 547 represents their mode of origin at the 

 anterior end of the proctodseum of a locust. 

 It will be seen that there are 10 primary 

 tubes. There are 150 such tubes in locusts, 

 or 10 groups of 15 each. The 15 second- 

 ary tubes probably arise from the primary 

 ones in the manner described by Hatschek 

 for Lepidoptera (see his Taf. Ill, Fig. 7). 



FIG. 547. Section of procto- While the Malpighian tubes usually first arise 

 o f f TSy^ubls'SSl as diverticula of the proctodaeum, in the Hymen- 

 p,%pkhelial or Vhmduiar layer; optera (Apis and Chalicodoma) they appear, even 



before the completion of the proctodamm, as 

 invaginations of the ectoderm which at first open 

 out on the outer surface of the primitive band. They seem, then, in some 

 degree, to be similar to the tracheal rudiments, which perhaps is the rea- 

 son why they have been homologized with them, a view which we do not share, 

 and in which Carriere does not concur. They afterwards pass, with the grow- 

 ing proctodaeuin, into the interior of the embryo. (Korschelt and Heider.) 



The heart. The dorsal vessel is first indicated, according to 

 Korotneff, by a long string or row of cells (cardioblasts) , which 

 on each side border the mesodermal layer of the primitive band 

 (Figs. 544, h, 548, /i). In the advancing growth of the primitive 

 band around the yolk, this rudiment steadily passes up more towards 

 the dorsal side. It is in connection with the wall of the primitive 

 segment (Figs. 544 and 548), and represents the point at which the 

 dorsal wall of the coelom-sac passes into the lateral wall. According 

 to Korotneff, the cardioblasts arise directly through a migration out 

 from the wall of the primitive segment. 



In Gryllotalpa the formation of the dorsal organ, which, as 

 Korotneff states, is in this insect nothing else than a stopper which 

 fills up the dorsal gap of the body-wall of the embryo, is effected by 

 the rupture of the embryonal membranes. The serosa is drawn 

 together to form a thick plate (Fig. 52.S, A, rp), and the much 

 degenerated amnion-folds (am) which are laterally attached to it 

 have moved from the edges of the primitive streak (*x-*y) far 

 towards the dorsal side (see Fig. 539, C, which represents a similar 



