PHOTOGENIC ORGANS OF LAMPYRIDS 153 



in the form of yellowish-brown granules. The affinity of phago- 

 cytes for the fat-body is a common feature during the meta- 

 morphosis of insects. It is claimed that phagocytes may pene- 

 trate the fat-body itself, but this does not occur in the case under 

 consideration. It must not be supposed that the photogenic 

 fat-spheres alone are thus affected, nor perhaps that they all 

 have such an investment. On the contrary, partial investment 

 and attraction of haemocytes is far more common in the fat- 

 spheres of the thoracic region and is rather infrequent elsewhere. 

 Probably the explanation for this is that in the thorax and in 

 the photogenic area, and perhaps also at the caudal extremity, 

 histolysis and histogenesis are much more vigorous than else- 

 where. In the head and thorax, at the time of pupation there 

 is a great alteration in the musculature and in the appendages, 

 and some in the nervous system, as well as a great alteration in 

 the body form, but these changes are not so pronounced in the 

 abdominal region, at least as regards the musculature. The 

 photogenic mass with its extensive tracheation must be quickly 

 built up over a large area. It is the direct product of the fat- 

 body, as we shall presently see. The haemocytes, FB, associated 

 with these fat-bodies are quite different — usually in size and 

 certainly in appearance — from the segmental blood-cells (figs. 

 17 and 18) . They were not recognized in larvae of the first instar, 

 where the segmental blood-cells were quite marked, but occurred 

 very abundantly in large larvae and in pupae. While the seg- 

 mental blood-cells are comparatively local, and perhaps rather 

 inactive, the fat-haemocytes, as we may term the others, have a 

 far more scattered distribution throughout the body and are 

 frequently in contact with some tissue. The segmental haemo- 

 cytes are on the average larger (8-13 micra), more regularly 

 rounded, deeply-staining granular cells, with large nuclei and 

 few or no vacuoles; the fat haemocytes on the other hand, are 

 usually smaller (5.8-12 micra), decidedly vacuolated and there- 

 fore of lighter color, with smaller, often irregular nuclei, and 

 though commonly spherical or nearly so, they frequently ex- 

 hibit amoeboid processes. 



