120 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



that of the fat cells. Since the cells in Apis have the same origin as the 

 cells of the paracardial strand of Forficula and Chalicodoma, Nelson 

 expresses the opinion that their homology can scarcely be open to question 

 although they are not connected in a strand. 



THE FAT BODY 



In the body cavity of insects, cell masses, in some cases loosely held 

 together, containing both fatty oil and proteid material constitute the fat 

 body. It is derived from the mesoderm and found in the embryo occupy- 

 ing the haemocoele in greater or lesser amount. In Locusta (Roonwal, 

 1937) the bulk of the median and lateral walls of the dorsal section of the 

 coelomic sacs from the second maxillary to the tenth abdominal seg- 

 ments, as well as the lateral wall of the dorsoanal pouch of the antennary 

 coelom, forms fat; but the labral, mandibular, and first maxillary meso- 

 derm sacs do not seem to share in this process. In Carausius, likewise, 

 fat is not formed by the first two gnathal sacs. In Calandra the fat 

 body, according to Tiegs (1938), occurs in two distinct parts: (1) a 

 bulky visceral portion occupying most of the haemocoele and in later 

 larvae almost obhterating it; (2) a comparatively inconspicuous parietal 

 zone of smaller less vacuolated cells, lying just under the epidermis and 

 external to the muscles. The main portion of the fat body is derived 

 from the inferior wall of the coelomic sacs from the labial to the ninth 

 abdominal segment. The parietal fat body arises independently of the 

 visceral and seems to be derived from cells originating in the external 

 walls of the coelomic sac. 



Nelson (1915) states that in the honeybee, ^vith the exception of 

 those in the pericardial chamber, the fat cells are formed from that part 

 of the visceral mesodermal layer which is not used up in the production 

 of the enteric muscles. This peculiarity is also shared by the mason bee 

 (Chalicodoma), so possibly it may be a condition prevailing among the 

 aculeate Hymenoptera, although Strindberg (19136) in his account of 

 the development of several species of ants belonging to the genera 

 Formica and Camponotus as well as of the termite, Eutermes rotundiceps, 

 and the beetle, Chrysomela hyperici, makes the general statement that 

 the fat body in these insects is derived from the somatic mesoderm, as 

 Heymons has found to be the case among the Orthoptera. The fat body 

 both in the haemocoele and in the pericardial chamber, then, seems to 

 be derived, with few exceptions, from the somatic mesoderm in insects 

 generally, including the apterygotes, as well as in the chilopods. 



THE PHOTOGENIC ORGANS 



There were, in general, two views as to the origin of the photogenic, 

 or light-producing, organs of the fireflies, or Lampyridae. According to 



