MICROORGANISMS IN THE EGG 141 



Curculionidae. — The discovery of the symbiotic relations between 

 certain bacteria and snout beetles is of recent date. Pierantoni (1927) 

 refers to a symbiotic organ in Calandra the same year that Mansour 

 (1927) described for the same species the ''accessory cell mass," later 

 (1930) recognized by Mansour as a mycetom, demonstrating the presence 

 of the symbionts (or commensals) in the female sex organs of older 

 embryos and in young larvae. Meanwhile Buchner (1927) had found 

 microorganisms in the genus Hylohius. A comparative study undertaken 

 by Scheinert (1933) revealed the presence of symbiotic bacteria in eggs 

 and larvae of a number of genera and species of snout beetles, among them 

 Hylohius ahietis and Liparus germanus. The conditions in these two 

 species are in most respects similar. In the larva of Hylohius an annular 

 mycetom is found on the alimentary canal between stomodaeum and 

 mid-gut. A dissolution of the structure takes place during pupal life. 

 In older adults mycetocytes are no longer to be found. The organisms 

 contained in them are probably discharged into the lumen of the mid-gut. 

 In recently deposited eggs the organisms may be seen distributed in the 

 yolk, abundant toward the anterior pole and in a thin concave-convex 

 lenticular mass near the posterior pole. In the outward migration of 

 cleavage nuclei those passing through the lenticular mass become laden 

 with the organisms, while numerous vitellophags remain behind in the 

 yolk. Cell walls soon form around the cytoplasmic zones that surround 

 the nuclei, the cells at the posterior end, the primordial germ cells, form- 

 ing a clump. In the manner just described the germ cells, both male 

 and female, become infected. Scheinert saw no evidence of a germ-track 

 plasm. Differentiation of the germ band and later of the inner layer 

 takes place. Under the blastoderm (future serosa) of the region not 

 covered by the germ band is a thin zone of organisms in which there are a 

 number of yolk cells spaced at approximately equal distances. Accom- 

 panying segmentation is a shifting and a shortening of the germ band 

 until the head lies near the anterior, the cauda near the posterior pole of 

 the egg. This change in position results in a displacement of the anterior 

 zone of symbionts into the anterior part of the yolk and where they are 

 irregularly distributed around the displaced yolk cells. At this time the 

 inner layer forms a continuous sheet; the germ cells lie irregularly 

 massed at the posterior end of the inner layer near the proctodaeal 

 invagination; and the stomodaeum is well advanced. The mid-gut 

 epithelium, too, begins to form as outgrowths from the blind ends of 

 stomodaeal and proctodaeal invaginations and hence are regarded as of 

 ectodermal origin by Scheinert in agreement with Mansour. 



When the stomodaeum has completed its growth, the blind end grows 

 out into a pointed process which apically unites with a plasmic sac-like 



