MICROORGANISMS IN THE EGG 139 



SYMBIONTS IN THE EMBRYO 



Coccidae. — Among the earliest references to the association of 

 symbiotic microorganisms with insects is material relating to the Coc- 

 cidae. Not until 1910, however, with the appearance of the works of 

 Sulc and Pierantoni, was the true nature of these organisms recognized. 

 Sulc demonstrated that the structure, to which Huxley many years 

 before applied the name ''pseudovitellus," was the seat of symbiotic 

 microorganisms. To the structure he applied the name "mycetom," 

 and to the cells containing the symbionts he gave the name "myce- 

 tocytes." Since then a number of works have appeared which were 

 summarized by Buchner (1930) on the symbiosis between animals and 

 plants in general and by Walczuch (1932) on the relation to coccids. 



The transmission of symbionts to the offspring in the coccids, accord- 

 ing to Walczuch (1932), always occurs within the body of the mother 

 through infection of the ovarian eggs. This type of transmission occurs 

 with other Homoptera as well as with Blattidae, Alallophaga, Siphun- 

 culata, Cimicidae, etc. With the Coccidae there are two ways in which 

 infection may occur. In the first type the symbionts enter the egg at the 

 base of the nurse cell by passage through or between the cells of the 

 follicular epithelium. This type of infection occurs with most Coccidae 

 and with the Cimicidae. The second type occurs with the coccid sub- 

 families Margarodinae, Orthezinae, Monophlebinae (except Marchalina), 

 and Lakshadinae in which infection takes place through the posterior 

 pole of the egg as with the Cicadellidae and other insects that bear 

 symbionts. 



The method by which the symbionts reach the egg differs with the 

 different genera of coccids. The direct entrance of the mycetocytes into 

 the egg folhcle, as in tha Aleurodidae, does not occur with the coccids, 

 where in the majority of cases individual symbionts wander into the egg 

 after being set free from the mycetocytes. The actual entrance of the 

 symbionts into the plasma of the egg occurs at different periods depend- 

 ing on the subfamily of the insect. With the Lecaniinae, Diaspinae, 

 Pseudococcinae, and Phaenococcinae maturation of the egg nucleus has 

 scarcely begun before symbionts begin to glide down the plasmic strand 

 from the nurse chamber; in the case of the Asterolecaniinae the symbionts 

 enter the egg after the second cleavage stage. The entrance of the 

 symbionts into the eggs of Tachardina and Cryptococcus takes place as 

 with the winter eggs of the Aphidae, as described below. 



Diverse also in the coccids is the origin of the mycetocytes and 

 mycetom. The mycetocytes of Tachardiella in large part are derived 

 from cleavage nuclei; those of Tachardina, from the yolk nuclei; the 

 mycetocytes of Orthezia are mesoderm derivatives. 



