212 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



clearly outlined, the optic plates are heavily pigmented, the tritocerebrum 

 is drawn up under the procephalon, and the buccal segments have drawn 

 forward in a more compact mass. 



Late in embryonic life a fusion of amnion and serosa occur as in many 

 insects; then contracting they form the secondary dorsal organ which 

 encloses the yolk on the dorsal side of the embryo. Gradually the enve- 

 lopes together with the yolk are carried into the mid-gut as the dorsal body 

 wall is being completed. 



Hagan did not study the earliest stages of Paratenodera sinensis. 

 Giardina (1897) described these stages in Mantis religiosa which probably 

 resemble those of the first-mentioned species. In M. religiosa three polar 

 bodies are given off at the periphery in the middle of the ventral side. 

 The female pronucleus leaving the periphery joins the male pronucleus 

 on its way toward the center. The fusion nucleus that results then 

 divides, the cleavage nuclei moving to the periphery, resulting in a 

 blastoderm. A little behind the middle on the convex side, a compact 

 mass of cells, the germ band, is formed but on the remainder of the surface 

 the cells are sparsely distributed. All cleavage nuclei reach the egg 

 surface, but later some migrate inward, first from the germ band but later 

 from the other part of the blastoderm, thus forming, especially under the 

 germ band, an inner layer of cells with large nuclei which divide amitoti- 

 cally. From this inner layer, cells free themselves to enter the yolk to 

 become yolk cells. 



Two longitudinal strips of mitotically dividing cells, which somewhat 

 diverge posteriorly and later become two or three layers deep, form on the 

 inner side of the germ band. The thin cells which do not take part in the 

 formation of the germ band now start to divide amitotically to give rise 

 to the serosa, whereas the amnion originates from the germ band by 

 mitotic division. Giardina did not describe the further formation of the 

 germ layers. From Rabito's account (1898) it appears that the mid-gut 

 epithehum in M. religiosa arises from the blind inner ends of the stomo- 

 daeal and proctodaeal invaginations as in Forficula. 



BLATTARIA 



The Croton Bug (Blattella germanica L.) 



This widely distributed cosmopolitan species has for many years been 

 a subject for embryological investigation by a number of workers. 



The eggs are enclosed in a purse-Hke capsule, or ootheca, within which 

 there are two parallel spaces, in each of which there is a row of separate 

 chambers each enclosing an egg. The ootheca is usually carried about 

 by the female until shortly before the emergence of the young. The 

 average number of eggs in an ootheca is about 30. The egg is elongate, 



