ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 71 



appear close round the surface of the nucleus, and in these a small granule 

 appears. They look like nuclei, in fact, and are termed by Blochmann 

 " neighbour-nuclei " (" Nebenkerne" j. They increase in number and the 

 principal nucleus becomes smaller. 



In the hitherto granular protoplasm a j)eculiar structure appears like a 

 much-coiled bundle of threads. They consist of regular rows of rod-like 

 bodies 10-12 {x, in length, like bacteria, and multiplying by division. At 

 an earlier stage similar bodies are seen in the epithelial cells. They 

 are dissolved in 5 per cent, soda solution, cannot be cultivated, and are 

 not bacteria. At the beginning of yolk-formation they retii'e to the posterior 

 pole and spread out under the blastoderm. After a while they pass into 

 cells of the embryo. They are not unlike the bacteroids developed in the 

 tubercles on leguminose roots and known to be albuminoid bodies. 



As the yolk appears the neighbour-nuclei are scattered over the surface 

 of the ovum, where they are for long visible among the yolk spheres, 

 eventually, however, disappearing. They have no connection with follicle- 

 formation. 



The yolk-formation occurs first in the portions next the follicular 

 epithelium. Vesicles appear, first with granules and then with a firm net- 

 work. These pass inwards, and the perij^heral ovum protoplasm forms 

 more. The so-called nutritive cells must aid in equip2:)ing the egg, but 

 there is certainly no reception of formed yolk-particles by the egg from 

 outside. A distinct yolk-nucleus was observed. 



The germinal vesicle retains its position at the anterior end of the ovum 

 and forms a nuclear spindle. Hints of a polar cell were detected. In 

 three different orders ;of insects Blochmann demonstrated the presence of 

 germinal vesicles, which does not agree with Stuhlmann's recent observa- 

 tions. In Musca vomitoria a polar cell was distinctly observed, and its 

 mode of formation was normal. 



In reference to the difficult problem of the relations of yolk, epithelial 

 cells and ova in insect oogenesis. Dr. J. H. List * communicates the result 

 of some observations on Ortliezia catapliracta. 



1. Each tubule exhibits a superior terminal yolk-chamber, and an 

 inferior egg-chamber. The latter is lined by high cylinder epithelium, 

 lower in the terminal chamber. 



The terminal chamber exhibits at an early stage, yolk flakes formed 

 from modified epithelial cells. Traces of the component cells are for a 

 while visible in the form of nuclei and cell-boundaries. The nuclei de- 

 generate, however, and are replaced by a new large nucleus. These yolk- 

 cells break down into yolk granules and form the yolk of the ovum. 



2. The ova arise from the epithelium of the egg-chamber, by a modi- 

 fication, perhaps budding of one, or rarely more of the lining cells. The 

 appearance at different stages is briefly noted. 



Origin and Significance of Cellular Elements of Ovary of Insects.f — 

 Dr. E. Korschelt concludes that the various cellular elements of the ovarian 

 tubes of insects — ova, nutrient cells, and epithelium — all arise from similar 

 indifferent elements, which are found in the contents of the first rudiment 

 of the tubes ; the first formation of the cells and the connected differentiation 

 of the several segments of the tube commence in the embryonic period; that 

 is, during larval life. The indifferent elements correspond to the embryonic 

 condition, and they in post-embryonic and even during imaginal life, con- 

 tinue to give rise to fresh supplies of the various kinds of cells. Different 



* Biol. Centralbl., vi. (1886) pp. 485-8. 



t Zeitschr. f. Wiis. ZooL, xliii. (1886) pp. 537-720 (.5 pis.). 



