Ill SPIRACLES HI 



system. They are called spiracles or stigmata. There is 

 extreme variety in their structure and size ; the largest and most 

 remarkable are found on the prothorax of Coleoptera, especially in 

 the groups Copridae and Cerambycidae. 



The exact position of the stigmata varies greatly, as does also 

 their number. In the Order Aptera there may be none, while 

 the maximum number of eleven pairs is said by Grassi ^ to be 

 attained in Jajpyx soUfugus : in no other Insect have more than 

 ten pairs been recorded, and this number is comparatively rare. 

 Both position and number frequently differ in the early and 

 later stages of the same Insect. The structure of the stigmata 

 is quite as inconstant as the other points we have mentioned are. 



The admission of air to the tracheal system and its confine- 

 ment there, as well as the exclusion of foreign bodies, have to be 

 provided for. The control of the air within the system is, 

 according to Landois '^ and Krancher,^ usually accomplished by 

 means of an occluding apparatus placed on the tracheal trunk a 

 little inside of the stigma, and in such case this latter orifice 

 serves chiefly as a means for preventing the , 



intrusion of foreign bodies. The occluding 

 apparatus consists of muscular and mechanical 

 parts, which differ much in their details in 

 different Insects. Lowne supposes that the 

 air is maintained in the tracheal system in a 

 compressed condition, and if this be so, this 

 apparatus must be of great importance in the ^ /-^ 



Insect economy. Miall and Denny ^ state Fiq. 61. Membranous 

 that in the anterior stigmata of the cock- and^meso-rhoraces^of 

 roach the valves act as the occluding agents, a beetle Euchroma, 



1 1 . ..ITT J.1 x ii showing stigma (<) ; 



muscles being attached directly to the inner ^^^ 1^1,^^ margin of 

 face of the valves, and in some other Insects pronotum ; b, front 



, ,, leg ; c, front margin 



the spiracular valves appear to act partially of mesonotum ; d, 

 by muscular agency, but there are many J^feTosternum*'^'' ' ^ 

 stigmata having valves destitute of muscles. 

 According to Lowne ^ there exist valves in the blowfly at the 

 entrance to the trachea proper, and he gives the following as the 

 arrangement of parts for the admission of air : there is a spiracle 



1 Mem. Ace. Lincei Rom. (4) iv. 1888, p. 554. 

 2 Zcitschr. wiss. Zool. xvii. 1867, p. 187. ^ Zool. Anz. iii. 1880, p. 584. 



'* The Cockroach, 1886, p. 151. ^ Anatomy of the Blowfly, 1893, p. 362 



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