No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 75 



servable in Corixa and probably also in Ranatra, of a small 

 quantity of yolk between the caudal amnion and the overlying 

 serosa when the embryo first passes to the dorsal surface, is 

 often observed in the Saltatoria. It is no great step to 

 pass from the conditions seen in the Hydrocorisa to the 

 " entoblastic " condition of other Hemiptera {Pediadus, Aphis, 

 Cicada) and the Odonata {Caloptcryx), where the germ-band 

 instead of passing to the dorsal yolk during anatrepsis, comes 

 to lie in the middle of the yolk, or even near the ventral 

 surface {Pyrrhocoris). The Thysanoptera, as may be in- 

 ferred from Jordan's brief statement ('SS), the Corrodentia 

 (Mallophaga) according to Melnikow ('69), and the Psocidse, 

 according to Packard ('84), are also referable to the "ento- 

 blastic" type. Concerning the embryonic development of the 

 Plecoptera and Dermaptera nothing is known. 



So far only the Homomorpha have been considered. The 

 eggs of the Heteromorpha, as I have attempted to show, con- 

 tain less yolk. Blastokinesis is nearly or quite lost in this 

 more recent group, a fact that perhaps indirectly tells in favor 

 of my view that the movements of the embryo have been ac- 

 quired for the purpose of ventilating the yolk and supplying 

 the growing embryo from time to time with fresh pabulum. 

 The transition to the Heteromorpha is probably represented by 

 the Ephemeridea. According to Burmeister's account of the 

 development of Palingcnia horaria (I quote from Zaddach, '54) : 

 ''am dritten Tage, nachdem das Ei gelegt war, hatte sich der 

 Keimstreif gebildet, der zungenformig war, und sich uber zwei 

 drittel der Eilange erstreckte, also in Form und Ausdehnung 

 ganz dieselben Verhaltnisse zeigte, wie im Phryganidenei." 

 This may, perhaps, be taken to indicate that the Ephemeridea 

 exhibit no blastokinesis; but the subject requires urgent 



investigation. 



Among the Heteromorpha it is especially the Coleoptera 

 which still show distinct though abortive movements of the 

 germ-band. Hydrophihis may be taken as an example. As 

 may be seen from Heider's figures, the germ-band forms on the 

 lower ventral surface of the ^^g. As it grows in length, and 

 the amnion is formed, the tail curls around the caudal pole on- 



