EMBRYOLOGY OF COCCIDS 105 



A special effort was made to locate the presence of the second 

 antenna! appendages and their ganglia, which were found and 

 described by Riley and others in Blatta germanica. My figure 

 114, which corresponds approximately to Riley's figure 5, shows 

 neither appendages nor ganglia. Throughout the embryonic 

 period there was no indication of the formation of the second 

 antennal appendages or the ganglia corresponding to them. 



The apparently later increase in size of the brain has already 

 been mentioned in connection with the formation of the external 

 form of the body. The statement, however, does not mean that 

 neurogenesis in this region lags behind that in the ventral nerve 

 cord. In fact, neurogenesis in the former occurs and progresses 

 just as early as in the second maxillary segment, and, conse- 

 quently, is ahead of that in the thoracic segment. In this regard, 

 then, coccids seem to differ from aphids, in which, according to 

 Will ('80), the brain arises independently from the ventral nerve 

 cord, as in the case of the annelids. 



Again, as my figures 62 and 67 show, the brain in coccids is 

 formed within and not beyond the rim of the blastopore, as Will 

 found in agamic aphids. 



8. THE INTRACELLULAR SYMBIOSIS 



Intracellular organisms in the eggs of scale insects have been 

 described under several different names, such as: Tseudonavi- 

 cellae' (Leuckart), 'secundaren Yolk' (Mecznikow), ''Highly re- 

 fractory bodies with specific gravity higher than water and may 

 represent spermatozoon" (Putnam), and 'Mycetomia' (Emeis). 

 The only investigator who denied the presence of such organisms 

 is Witlaczil, while Johnston, Child, and other students of the 

 internal anatomy of coccids failed to mention either their presence 

 or absence. 



Mention has already been made of the presence of an organism 

 in the mealy bug, in the cottony cushion scale, and in Lecanio- 

 diaspis prunosa. These bodies present an appearance of true cells 

 at certain times in their history, but they more often stain heavily 

 and hence look like granules. Whenever they assume a true 

 cellular form, a cell membrane, chromatic granules, and cytoplasm 



