230 



ANNUL AT A. 



vertebrates. Some points of special interest in the subsequent develop- 

 ment are the presence of a segment between that of the antennae and 

 that of the mandibles, and the presence of abdominal appendages which 

 disappear later. These seem to point to the cockroaches having sup- 

 pressed a head segment, probably corresponding to that bearing the 

 antennce in the lobster, and to their having in a similar way lost a 

 number of abdominal appendages. 



The mesoblast is present in the embryo as paired somites containing 

 coelomic cavities, separate from the hsemocoele or blood-space, part of 

 which forms the heart. In later development, however, the mesoblast 

 walls break up to form the muscles, connective tissue, gonads and 

 walls of the heart ; the cavities of the somites then become continuous 

 with the haemocoele. Thus there is no true perivisceral coelom in the 

 cockroach, a condition agreeing with other Arthropoda. 



The young cockroach only differs from the adult by an 

 absence of wings, and it grows gradually into the adult, pass- 

 ing through periodic ecdyses or shedding of its integument. 

 Hence the cockroach is ametabolic^ or developing without 

 metamorphosis. 



BLATTA. 



