MODE OF HATCHING 583 



n. The process of hatching 



This has been observed only in a few cases, and careful observa- 

 tions as to the exact manner in which the embryo breaks the egg- 

 shell and frees itself from the amnion are much needed. Also the 

 rapid changes of form from that of the embryo within the egg-shell, 

 and that which it immediately assumes after breaking forth from 

 the shell and membranes, have yet to be observed ; for these will 

 undoubtedly be found to have special phylogenetic significance. 

 Indeed, the phylogenetic importance of the latest embryonic changes 

 in insects just entering on the nymph or the larval stages is very 

 great, though little attention has as yet been bestowed upon the 

 matter. 



As regards the changes at the time of hatching, Wheeler tells us 

 that the cockroach (Phyllodromia), shortly after leaving its narrow 

 place in the egg-capsule, undergoes a peculiar change in shape. 

 Before hatching, and when confined in the egg-shell, the body is 

 about one-third as wide as thick ; but soon after breaking out of the 

 chorion its body is much flattened, its dorso-ventral diameter being 

 only about a third as great as its greatest breadth. This shows that 

 the flattened shape of the body of cockroaches, which adapts them 

 for their life under bark and stones, is a very late inheritance, and 

 that these insects have descended from those with more cylindrical 

 bodies. The end of the body, also, which in the egg is bent under- 

 neath the abdomen, is, after hatching, bent dorsally, as indicated 

 by the anal stylets, which now point directly upwards and outwards. 

 The spines and claws are developed shortly before hatching. In 

 the Locustidse (Xiphidium, etc.) Wheeler has observed that the 

 pleuropodia, or 1st pair of abdominal temporary embryonic append- 

 ages, are shed during hatching. All the other embryonic append- 

 ages have also disappeared, except those which persist and have 

 rapidly become modified to form the cercopods, or the ovipositor. 



In locusts, as we have observed l in the case of Melanoplus spretus, 

 the egg-shell bursts open at the head end, when the nymph, imme- 

 diately after extricating itself from the egg, casts off a thin pellicle 

 (the amnion), as we have also noticed in the case of the larvae of the 

 flea, currant saw-fly, and other insects. Before the amnion is cast 

 off, the young nymph is almost motionless, but by slight movements 

 of the body draws itself, in about five minutes, out of the amnion. 

 The exact process of extraction is as follows : While it lies motion - 



1 Report on the Rocky Mountain locust, etc. Ninth Annual Report U. S. Geol. and 

 Geogr. Survey of the Territories for 1875, pp. 633, 634. 



