No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 25 



this flexure always takes place between the 7th and 8th seg- 

 ments and is brought about during the shortening of the 

 embryo. It is essentially the same flexure which is found in 

 Blatta and in Decapod Crustacea. 



In Stage G the antennae have increased to nearly one-third 

 the length of the embryo. The procephalic lobes on which the 

 segmentation of the brain is plainly visible, have developed 

 greatly. The appendages, instead of projecting laterally, as 

 they do in the younger embryo, are folded over the ventral 

 surface of the germ-band. The nerve cord is distinctly 

 marked out. (See abdominal region. Fig. 7.) 



It is in this stage, or one but slightly more advanced, that 

 the embryo passes the winter. Cleavage and the succeeding 

 stages up to F are passed within a month after oviposition — 

 during the warm days of August and September. But even 

 should October and November be mild and sunny, development 

 seems to have come to a temporary standstill on reaching 

 Stage G. Among the hundreds of embryos which I collected 

 during three succeeding autumns, I did not find one that had 

 passed far beyond this stage. Nevertheless if kept in a warm, 

 moist atmosphere during winter, a certain number of eggs 

 will continue their development almost to hatching. 



Before passing on to later stages in the development I will 

 here give a brief account of some anomalies in the development 

 of the indusium. 



4. Variations in the Development of the Indiisiuni. 



In the preceding pages I have described what I take to 

 be the normal development of the indusium of Xiphidiiim. 

 A considerable number of embryos (about 100), being nearly 

 one half of the total number examined for the stages thus far 

 described, deviated more or less widely in so far as the in- 

 dusium was concerned from what I consider the normal type of 

 development. Unfortunately I did not discover the organ till 

 it was too late in the season to obtain a large supply of material 

 in the requisite stages, so that the variations here briefly 

 noticed probably represent only a small fraction of those 



