TiiK i)evelopmp:nt of insects. 



57 



Tous cord is represented by eight or nine large oblong-square 

 'seen sideways) ganglia, which lie contiguous to each other. 



The formation of the eyes, the post-abdomen, the sternites, 

 and median portion of the nervous cord seems nearly synchro- 

 nous with the closing up of the dorsal walls of the body, though 

 the division of the tegument into segments has not apparently 

 taken place over the yolk-mass. 



The succeeding stage (Fig. 59) is signalized by the appear- 

 ance of the rudiments of the intestine, i a 2 e 

 while the second maxillne are directed 

 more anteriorly. 



In form the body is ovate-cylin- 

 drical, and there is a deep constric- 

 tion separating the post- abdomen 

 from the anterior part of the abdo- 

 men. A 7 6 5 4 ic 



The terminal (eleventh) ring is ^''°- ^^• 



immensely disproportioned to its size in the embryo just pre- 

 vious to hatching (see Fig. 61, where it forms a triangular piece 

 ^ 5 6 7 situated between its appendages, 



the anal stylets). At a later 

 period of this stage two more ab- 

 dominal segments have been added, 

 one to the end of the main body 

 of the abdomen, and another to 

 the post- abdomen. They have 

 been apparently interpolated at the 

 junction of the post-abdomen to 

 the abdomen proper. Should this 

 observation be proved to be correct, it may then be considered 

 as a rule that, after reaching a certain number of segments, all 

 additional ones are interpolated between the main body of the 

 abdomen and its terminal segment or segments. This is the 

 law of increase in the number of segments in Worms, and in 

 Myriopods {Mm, according to Newjoort's observations), in 

 Arachnids (Claparede), and Crustacea (Rathke). 



The next stage (Fig. 60), is characterized by the differentia- 



FiG. 59. An embryo much farther advanced, c, clypeus; E, eye; a, bi-lobed 

 extremity of the abdomen; 1, the rudiments of the intestines. 



