274 GENERAL ANATOMY OR HISTOLOGY OF BLOW- FLY. 



The best part for the demonstration of this tissue is the 

 thin wall of the great abdominal air sacs, which is covered by 

 a network of flat stellate cells. Tufts of branching cells, also 

 belonging to the reticulum, are found on the terminal branches 

 of the tracheal vessels, and sections exhibit it in the blood 

 sinuses and between the muscles. 



The evidence on which it is believed that this adenoid reti- 

 culum is developed from the parablast, although not direct in 

 Insects, is on the whole very conclusive. It is precisely similar 

 to the parablastic tissue of the Echinodermata and Coelente- 

 rata described by Hertwig, Kjrotneff, and others. In parts of 

 the body, more especially in the pericardium, it is converted 

 into a true cytogenic tissue, from which amoeboid leucocytes 

 are developed. It is very abundant in the coelom of the nymph, 

 and is apparently formed by the metamorphosis of the leuco- 

 cytes, which abound at this period, and the corresponding 

 tissue in the larva originates from the deep cells which lie 

 beneath the blastoderm, and not from the cells of the coelomic 

 pouches. Lastly, Schaffer [131] has traced the development of 

 leucocytes to the peritoneal coat of the tracheae, and to groups 

 of cells closely related to, and probably merely a part of, the fat 

 bodies. 



The Fat Bodies of the larva have already been described 

 (p. 85). Those of the imago are subcutaneous groups and 

 strings of multinucleate cells. 



Three kinds of cells have been described in the fat bodies of 

 many Insects — Fat cells. Intercalated cells {EingcsprcngtcZcUen, 

 Oinocytes), and Cytogenic cells (Blut-heerde). 



The fat cells of the larva become cytogenic in the pupa, but 

 whether from the immigration of leucocytes which multiply in 

 their interior, or by actual proliferation of their nuclei, is a 

 matter which cannot be definitely settled (see Chap. IX.). In 

 the Blow-fly larva the oinocytes appear to be distinct from the 



skin of Corethra larvie by Wielowiejski, Zool. Anzeig. 6 Jahr 9. A typical 

 example of the formaiion of intracellular canals is seen in the development 

 of the capillaries of Vertebrates, and the tracheal capillaries of Insects are 

 developed in a precisely similar manner. 



