74 



The Larva of Chivonomiis 



Devel.>r- 

 inent of 

 tlie dorsal 



vessel. 



meshes, wliich apjDears to be attached to the ventral side 

 of the heart ; a large multinucleate pericardial cell, 

 elongated in the direction of the dorsal vessel, overlies 

 each of these expansions. There are also small pericardial 

 cells, which are attached to the upper surface of the same 

 alary tendons singly or in clusters. They are uninucleate, 

 and contain oil-drops, as well as minute brownish concre- 

 tions, probably fatty (Wielowiejski). Kowalewsky has 

 discovered indications that the pericardial cells perform 

 an excretory function. They eliminate carminate of 

 ammonia, and have an acid reaction. A very small cell 



cam. 



Fig. 55. — Part of dorsal vessel of larva, with pericardial cells 

 and alary muscles of one segment, am, alary muscles. 

 i>c, pericardial cell, n, nucleus. 



or nucleus (perhaps a nerve-cell) is found near the middle 

 of each alary muscle. The aorta is held in place by 

 a great number of very fine threads which pass to its 

 dorsal side from the body-wall. 



The stomato-gastric nerves of the aorta are described 

 on p. 48. 



All Chironomus-larvae do not exhibit the same structure 

 of the dorsal vessel, and the variations cannot be fully 

 understood without some knowledge of the development 

 of the organ. We learn from Jaworowski (1879) ^^^ 

 G-raber that the heart of an insect (Pj^rrhocoris) may 

 during embryonic development take the form of a nearly 



