TR AC 11 EAT 'A. 



341 



Although in the 

 between the pro- 

 thorax and head 1 , 

 in the embryo 

 and the larva 

 tracheal invagi- 

 nations may be 

 developed in all 

 the thoracic (and 

 possibly in the 

 three jaw-bearing 

 segments) and in 

 all the abdominal 

 segments except 

 the two posterior. 



In the embryo 

 of the Lepidoptera, 

 according to Hat- 

 schek (No. 414), 

 there are 14 pairs 

 of stigmata, belong- 

 ing to the 14 seg- 

 ments of the body 

 behind the mouth; 

 but Tichomiroff 

 states that Hat- 

 schek is in error 

 in making this 

 statement for the 

 foremost post-oral 

 segments. The 



last two segments 



a 



dult 



stigmata 



are never found in the space 



n/n 



VII 



am 



sf 



me.s 



stig- 



FIG. 189. THREE TRANSVERSE SECTIONS THROUGH THE 

 EMBRYO OF HYDROPHiLus. (After Kowalevsky.) 



A. Transverse section through the larva represented in 

 fig. 187 A. 



B. Transverse section through a somewhat older embryo 

 in the region of one of the stigmata. 



C. Transverse section through the larva represented in 

 fig. 187 B. 



vn. ventral nerve cord ; am. arnnion and serous mem- 

 brane ; me. mesoblast ; me.s. somatic mesoblast ; hy. hypo- 

 blast (?); yk. yolk cells (true hypoblast); st. stigma of trachea. 



are without 

 mata. In the larva? 

 of Lepidoptera as 

 well as those of 

 many Hymenoptera, Coleoptera and Diptera, stigmata are present on all 

 the postcephalic segments except the 2nd and 3rd thoracic and the two last 

 abdominal. In. Apis there are eleven pairs of tracheal invaginations ac- 

 cording to Kowalevsky (No. 416), but according to Biitschli (No. 405) only 

 ten, the prothorax being without one. In the Bee they appear simul- 

 taneously, and before the appendages. 



The blind ends of the tracheal invaginations frequently (e.g. Apis) 

 unite together into a common longitudinal canal, which forms a 

 longitudinal tracheal stem. In other cases (e.g. Gryllotalpa, Dohrn, 

 No. 408) they remain distinct, and each tracheal stem has a system 

 of branches of its own. 



1 In Smynthurus, one of the Collembola, there are, according to Lubbock, only two 

 stigmata, which are placed on the head. 



