EMBRYOLOGY OF COCCIDS 109 



The symbiotic organisms in Homoptera were first discovered 

 in the pathogenetic embryo of aphids by Huxley ('58). Meczni- 

 kow ('66) detected a similar substance not only in the embryos 

 of aphids, but also in those of coccids and Psylla. This writer 

 thought his 'secundaren Dotter' to be characteristic of three 

 families of Homoptera, namely, Aphididae, Coccidae, and Psylli- 

 dae. Witlaczil ('84) and Will ('88) confirmed the presence of 

 ■pseudovitelli' so far as the parthenogenetically developing 

 embryos of aphids are concerned. The occurrence of similar 

 granules in the winter or sexual eggs of Aphids was first reported 

 by Balbiani ('74) and was later confirmed by the researches of 

 Tannreuther ('07) and Webster and Phillips ('12). All of these 

 writers, however, did not consider these as living organisms. 

 Huxlej^ ('58) was also the first who described the origin of the 

 'pseudo\dtellus.' He states that- the pseudova (partheno genetic 

 eggs) of Aphids are eventually converted into cellular germs, 

 apparently by the same process as that bj' which an ovum is con- 

 verted into an embryo. '"In these germs," he claims, "the 

 central part becomes a granular pseudo^dtellus, the peripheral a 

 blastoderm; the rudiments of the different organs next appear, 

 and the germ becomes surrounded by a pseudo\'itelline membrane. 

 Eventually," he supposed, ''the pseudovitellus becomes the 

 corpus adiposum. " 



]\lecznikow ('66), however, observed the origin of the pseudo- 

 vitellus in aphids. He stated that the so-called secondary yolk 

 comes from the follicular cells situated at the posterior end of the 

 egg. This discovery was later confirmed by Witlaczil ('84) and 

 Will ('88). 



Emeis ('15) recently found a case of sj-mbiosis in the eggs of 

 Coccids. These symbiotic JNIycetomia were first found in a 

 certain epithelial cell near the nurse cells. Later, according to 

 him, they migrated into the protoplasmic portion of the egg. 

 Their subsequent history has, however, not been studied. 



Inclusions other than the secondary yolk, but somewhat related 

 to this substance, were recorded for insects belonging to several 

 different orders. Blochman ('87) noticed a group of bacteria- 

 like organisms which he called bacterial 'Stabchen' in the eggs 



