(91) 



STRUCTURE, DEVELOPMENT, AND BIONOMICS OF HOUSE-FLY. 531 



action of this posterior cardiac region of the dorsal vessel. 

 Lowne describes other openings in the wall of the "heart" 

 of the blow-fly larva, but I have been unable to find others 

 than those already described in this larva ; it has three pairs 

 only. 



The dorsal aorta is the anterior continuation of the dorsal 

 vessel, which gradually diminishes in diameter. When it 

 reaches the fifth segment and lies above the ganglion, it ter- 

 minates in a peculiar cellular structure (fig. 24,. c. r.) } which 

 in the blow-fly has a circular shape and was called by 

 Weismann the "ring." In the larva of M. domes tica it 

 has not so pronounced a ring-like appearance, but is more 

 elliptically compressed and rather A-shaped. The cells of 

 which it is composed have a very characteristic appearance, 

 and are rather similar to a small group of cells lying on the 

 neck of the proventriculus and at the anterior end of the 

 dorsal vessel of the fly. From the lower sides of this cellular 

 structure (fig. 28, c. r.) the outer sheaths of the major cephalic 

 imaginal discs depend, and extend anteriorly to the pharyngeal 

 mass, enclosing between them the anterior portion of the great 

 ventral blood sinus. 



The pericardium lies in the four posterior segments of the 

 body, and is delimited ventrally from the general body-cavity 

 by a double row of large characteristic pericardial cells. These 

 cells have a fine homogeneous structure and are readily dis- 

 tinguished from the adjacent adipose tissue cells, whose size 

 they do not attain. The pericardial cavity contains a profuse 

 supply of fine tracheal vessels which indicates a respiratory 

 function. A similar condition occurs in the blow-fly larva, and 

 Imms (1907) has described a rich pericardial tracheal supply 

 in the larva Anopheles maculipennis, as also Yaney (1902) 

 and Dell (1905) in the larva of Psychoda punctata. The 

 adipose tissue cells (fig. 28, /. c.) form the very prominent 

 "fat-body." They are arranged in folded cellular lamina 

 that lie chiefly in the dorso-lateral regions of the body, and in 

 section have the appearance shown in the figure. The cells 

 have a similar structure to those of the adult fly; they are 



