474 



has described as occurring in Doryphora (Wheeler '89, pp. 356-358), 

 but sections of the embryo at this stage do not show anything that 

 would lead me to believe that it is absorbed into the yolk. The ab- 

 sence of such a structure in Camponotiis illustrates one striking dif- 

 ference between the development in that genus and in Myrmica. In 

 Camponotus the amnion becomes the dorsal body-wall. 



At this age the segments are more deeply constricted off from 

 each other. The three pairs of mouth parts are further developed, 

 and the thoracic and abdominal appendages are present, although in 

 a side view it is difficult to distinguish them from the body segments. 



In the stage represented by Figure 33, the embryo is seen to be 

 straightening somewhat, the posterior and anterior ends being farther 

 apart. The segments are still more deeply constricted off from each 

 other, and the lateral edges of the germ band have grown dorsad 

 until they have almost completed the dorsal closure. The invagina- 

 tion of the stomodseum has grown farther inward, the posterior 

 end of the stomodseum almost reaching the yolk. On the sides of 

 the procephalic lobes appear the small tubercle-like thickenings which 

 represent the antennae. The labrum and the three pairs of mouth 

 parts more closely approximate each other and tend to bend in over 

 the opening of the stomodseum. This is shown better in Figure 34, 

 which represents a frontal view of the same stage. 



In the stage represented by Figure 35, the embryo has straight- 

 ened still more, and the dorsal closure has been completed. The 

 mouth parts still more closely approximate each other and bend in 

 over the stomodseum. The thoracic and abdominal appendages have 

 disappeared, as have also the antenn?e. The stomodseum and procto- 

 deeum extend inward as far as the yolk, which is now enclosed in 

 the somewhat pear-shaped mesenteron. The ventral segments are 

 constricted off into blocks, three pairs in the thorax and seven in 

 the abdomen, the last three abdominal segments having united to- 

 gether. In each of these segments a primitive ganglion is evident, 

 and in the last abdominal segment three ganglia appear, showing the 

 compound nature of the segTnent. In the head region three separate 

 ganglia can be distinguished, for the suboesophageal ganglion appears 

 in the whole embryo to be all in one part. 



Figure 36 represents a stage just before the tgg hatches, when the 

 embryo has practically the form of the young larva. The embryo 

 has now bent completely over so that the flexure, instead of being 

 on the dorsal side as before, is on the ventral side. The thoracic 

 region has lengthened considerably. The mouth parts are in their 

 normal position for the larva and have practically the same form. 



