EMBRYOLOGY OF COCCIDS 107 



The parasites, thus finally collected into a single mass, remain 

 at this position throughout the embryonic as well as the larval 

 and adult life. This place, it should be mentioned, corresponds 

 to the third to fourth abdominal segments of the future embryo 

 and adult. 



After the completion of the blastoderm and the subsequent 

 invagination of the germ band (which occurs at about the pos- 

 terior end of the egg) , the germ cells, the first differentiated cells, 

 migrate toward, and some of them actually become imbedded in 

 this colony of symbiotic organisms. Of the migratory cells, 

 those which become imbedded in the mass of parasitic organisms 

 are transformed into the secondary yolk cells of Will ('88). The 

 nuclei of the secondary yolk cells remain almost unaffected for a 

 long time, even after hatching. Again, some of the cells surround- 

 ing the colony of organisms transform into epithelial cells, while 

 a majority of them divide, multiply and finally become the defin- 

 itive germ cells. 



As previously stated, the invaginating germ band gradually 

 increases in length until the caudal region becomes actually 

 curled over the thoracic region, but the colony of symbiotic 

 organisms remains almost stationary at the place where it was 

 first located soon after the entrance into the egg. This fixed place, 

 as pre\dously stated, corresponds approximately with the third 

 and fourth abdominal segments of the future embryo and also 

 of the larva and adult. 



From this time on, the spherical colony of organisms, consisting 

 of about eight compartments of spores, becomes spread out over 

 the rudiments of the ovaries. The organisms gradually increase 

 in number after hatching until they fill the greater portion of the 

 coelomic area of the adult females. 



These organisms are also found in enormous numbers, simi- 

 larly located, in the larval as well as the adult males. From the 

 fact that these organisms remain throughout the life history of 

 the scale insects, I strongly believe that they are not sperm cells 

 as Putnam ('88) surmises. It also clearly shows that they do 

 not function as 'Keimbahn determinants' as Mecznikow doubted 

 in the case of Psylla. 



