234 HAROLD R. HAGAN 



completely from actual contact with each other or with the body 

 except at the points of articulation. This covering cannot be 

 the vitelline membrane or the chorion, as either of these would 

 appear as a simple sac enclosing the body and appendages. 

 According to Phil and Nellie Eau ('13) this covering is a simple 

 sac enclosing the embryo and binding the appendages (except 

 the prothoracic legs) to the body. They suggest that the first 

 pair of legs, project through this envelope and are therefore free. 

 I find that Muir and Kershaw ('12)* sometime ago pointed out 

 the common error of supposing this cuticle to be amniotic in 

 origin. This membrane exhibits ridges, pits and spines on its 

 exterior surface due to the conformations of the hypodermis 

 which secretes it. The front of the head is produced considerably 

 to form an organ which aids by its alternate contraction and 

 expansion, in the escape of the animal when hatching and emerg- 

 ing from the ootheca. In function it is clearly analgous to the 

 ptilinum of the higher Diptera. Over this area the envelope 

 is very materially thickened, possibly for protective purposes. 

 At the posterior end the tips of the envelope covering the cerci 

 are connected, each by a slender thread, to the egg membranes. 



The first ecdysis. Hatching is accomplished by alternately 

 contracting the dorsal and ventral parts of the body with a sort 

 of undulatory motion. Shortening the ventral surface pulls 

 forward the dorsal segments, and reversing the movement ad- 

 vances the ventral parts and the appendages. The return of 

 the segments to their former positions is prevented by their 

 strongly chitinized hind margins and the posteriorly directed 

 spines and bristles, particularly on the legs and cerci. At this 

 time the partially flexed portion of the abdomen becomes straight- 

 ened posteriorly. 



After hatching, the insect is suspended by the two threads 

 attached to the posterior part of the epidermis. While hatching 

 it has increased in length and, almost as soon as it is hanging 



Text fig. 2 The dorsal organ and the indusium. A, sagittal section of the 

 embryonic rudiment through the appendages and the indusium. This stage 

 is a little later than that of figure 2. The embryonic envelopes are slightly dia- 

 gramatic, being shortened and not following the outlines of the embryonic rudi- 



