380 



INSECT A. 



tissues fully capable of vital activity, e.g., those of the imaginal discs, 

 resist the attack of the leucocytes, the larval tissues, less capable 

 of vital activity, are broken up into fragments by the attack of 

 the leucocytes, and are simply devoured and digested by them. 

 These processes may best be followed in the disintegration of the 

 larval musculature. The destruction of most larval organs is thus 

 due to the capacity for the taking in of nourishment and for intra- 

 cellular digestion possessed by the amoeboid blood-corpuscles. This 

 capacity has been specially emphasised by Metschnikoff (Nos. 116 

 and 117), who with reference to this significance of the blood- 

 corpuscles has called them phagocytes. 





.-■-« 



«•".«%>?» «?*V7{«,*? 



MMZfc 





ss?s 



m 



Fig. 1SS. — Sections through a hypodermal imaginal disc in the abdomen of Mv&m (after 

 Kowalevsky). A, through the larva. B and C, through the pupa, h, larval hypodermis ; 

 h', detached portions of the same attacked hy phagocytes ; i, imaginal disc ; fc, phagocytes 

 containing disorganised hypodermal cells (so-called granular cells); k', phagocytes enclosing 

 hypodermal nuclei ; m, mesodermal rudiment of the imaginal disc ; w, wandering cells. 



The re-formation of the hypodermis is accomplished in the head 

 and in the abdomen in the same way as in the thorax. In each 

 of the eight segments of which the abdomen of the larva consists, 

 there are, according to Ganin (Xo. 107), four islands of small cells; 

 these are the imaginal discs (Figs. 187, hi, and 188, i) from which 

 the re-formation of the hypodermis proceeds. Van Rees has recently 

 discovered another pair of small imaginal discs on the abdominal 

 segments. The four discs that occur on the last body-segment, 



