ANATOMY AND PHYSIOLOGY 



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cavity. The distribution of the fat-body is to a certain extent definite, 

 however, for the fat-tissue conforms to the general segmentation and is 

 arranged in each segment with an approach to symmetry. Much of this 

 tissue forms a distinct peripheral layer in each segment, and masses of 

 fat-body occur constantly on each side of the alimentary tract and also at 





FIG. 163. Transverse section of the abdomen of a caterpillar, Pieris raps, b, blood cor- 

 puscles; c, cuticula; d, dorsal vessel; /, fat-body; g, ganglion; //, hypodermis; /, leg; m, 

 muscle; ml, mid intestine, containing fragments of cabbage leaves; mt, Malpighian tube; s, 

 silk gland; sp, spiracle; tr, trachea. 



the sides of the dorsal vessel, in the latter case forming the pericardia! 

 fat-body. 



Fat-Cells. The fat-cells (Fig. 164) are large and at first more or less 

 spherical, with a single nucleus (though there are said to be two in Apis 

 and several in Musca), but the cellular structure of the fat-tissue is often 

 difficult to make out because the cells are usually filled with globules of 

 fat (Fig. 165), while old cells break down, leaving only a disorderly net- 

 work. The fat-cells sometimes contain an albuminoid substance, and 



