J34 



CIRCULATION 



valvular structure. In Cimbex she finds a similar arrangement, 

 but there are ten chambers, and no aorta. 



The dorsal vessel is connected with the roof of the body by 

 some short muscles, and is usually much surrounded by fat-body 

 into which tracheae penetrate ; by these various means it is kept 

 in position, though only loosely attached ; beneath it there is 

 a delicate, incomplete or fenestrate, membrane, delimiting a sort 

 of space called the pericardial chamber or sinus ; connected with 

 this membrane are some very delicate muscles, the alary muscles, 

 extending inwards from the body wall (&, Fig. 72): the curtain 

 formed by these muscles and the fenestrate membrane is called 



FIG. 72. Dorsal vessel 

 (c), and alary muscles 

 ( 6),of Gryllotalpa ( after 

 Graber) ; a, aorta. 

 N.B. The ventral 

 aspect is here dorsal, 

 and nearly the whole 

 of the body is removed 

 to show these parts. 



FIG. 73. Diagram of transverse section 

 of pericardial sinus of Oedipoda coeru- 

 lescens. (After Graber, Arch. Mikr. 

 Anat. ix. ) H, heart ; s, septum ; in, 

 muscles the upper suspensory, the 

 lower alary. 



the pericardial diaphragm or septum. The alary muscles are 

 not directly connected with the heart. 



It has been thought by some that delicate vessels exist beyond 

 the aorta through which the fluid is distributed in definite 

 channels, but this does not appear to be really the case, although 

 the fluid may frequently be seen to move in definite lines at some 

 distance from the heart. 



There is still much uncertainty as to some of the details of 

 the action of the heart, and more especially as to the influence of 

 the alary muscles. The effect of the contraction of these must 

 be to increase the area of the pericardial chamber by rendering 



