24 WHEELER. [Vol. VIII. 



treme anterior pole of the ^gg. I confess, however, that my 

 observations on this envelope are rather unsatisfactory. 



After the completion of the processes described in the 

 preceding paragraphs we may distinguish several envelopes 

 in a median transverse section of the egg. Passing from with- 

 out inwards we have (i) the chorion, (2) the Blastodermhaut- 

 like cuticle secreted by the serosa, (3) the serosa, (4) the 

 outer indusium, (5) the layer of dark, granular secretion, (6) 

 the cuticle secreted by the inner indusium, (7) the inner 

 indusium and (8) the amnion. While envelopes 1-7 invest 

 the whole egg, layer 8, the amnion, covers only the embryo. 



The general development of the embryo has been traced to 

 Stage F, when it lies as a straight and attenuated body on the 

 dorsal yolk with its head directed towards the caudal and its 

 tail towards the cephalic pole of the ^gg. 



Like all other insects that have a stage during which the 

 body is greatly elongated (Coleoptera, Diptera, Lepidoptera) 

 XipJiidiiim passes into a series of stages during which the 

 germ-band is gradually shortened. The shortening is accom- 

 panied by a broadening of all the segments, a growth of the 

 appendages, and very important internal changes. The com- 

 pletion of this process is reached in Stage G (Fig. 7). Besides 

 a greater development of the appendages seen in Stage F, Fig. 

 7 also shows that the abdominal appendages have appeared. 

 Of these there are nine pairs, exclusive of the pleuropodia 

 and cerci, so that in Xiphidium, just as in Blatta and many 

 other insects, every segment of the abdomen bears a pair of 

 appendages. Starting with the basal segment there are eight 

 pairs of stigmata. These are not all seen in the figure. Just 

 back of each pair of tracheal invaginations appears a second 

 pair of ingrowths — the metastigmatic depressions — seen as 

 small white spots just outside the appendages, near the pos- 

 terior edges of their respective segments. They are in line 

 (homostichous) with the tracheal invaginations which occupy 

 corresponding positions near the anterior edges of their 

 respective segments. 



The ventral flexure of the abdomen constitutes another very 

 important difference between Stages G and F. In Xiphidium 



