32 THE COCKROACH : 



first, and the apodeme is formed in the midst of a group of 

 chitinogenous cells distant from the superficial layer, though 

 continuous therewith. Many tendons of insertion are formed 

 in this way. The two forked processes in the floor of the thorax 

 (p. 58, and fig. 27) are unusually large and complex structures of 

 the same kind. In the tentorium of the head (p. 39, and fig. 17) 

 a pair of apodemes are supposed to unite and form an extensive 

 platform which supports the brain and gullet. 



Fig. 11. Nymph (in last larval stage) escaping from old skin. X 2|. 



Like other Arthropoda, Insects shed their chitinous cuticle 

 from time to time. A new cuticle, at first soft and colourless, is 

 previously secreted, and from it the old one gradually becomes 

 detached. The setae probably serve the same purpose as the 

 " casting-hairs ' described by Braun in the crayfish, and by 

 Cartier in certain reptiles,* that is, they mechanically loosen the 

 old skin by pushing beneath it. In many soft-bodied nymphs 

 the new skin can be gathered up into a multitude of fine 

 wrinkles, which facilitate separation, but we have not found 

 such wrinkles in the Cockroach, except in the wings. The 

 integument about to be shed splits along the back of the 

 Cockroach, from the head to the end of the thorax,*f* and the 

 animal draws its limbs out of their discarded sheaths with much 

 effort. It is remarkable that the long, tapering, and many- 

 jointed antennae are drawn out from an entire sheath. At the 



* A condensed and popular account of these researches will be found in Semper's 

 Animal Life, p. 20. 



+ Prof. Huxley (Anat. Invert. Animals, p. 419) states that the integument splits 

 along the abdomen also, but this is a mistake. 



