422 SUMMAKY OP CURRENT RESEARCHES RELATING TO 



(/) Formation of Lecithin. — In the protoplasm, at first homogene- 

 ous, dark granules appear near the nucleus. These are unchanged 

 by acetic acid, and have been formerly termed protoplasmic granules. 

 After these, lecithin-granules are formed, which are clarified by acetic 

 acid. They are at first clear, like spaces filled with a drop of fluid, 

 and gradually assume dark, fat-like contours. 



The epithelial cells persist till the eggs are laid, and then dis- 

 appear. There is nothing to show that the contents of the yolk-cells 

 are taken into the egg. 



(g) Disappearance of germinal vesicle. — In all cases the germinal 

 vesicle becomes invisible. In Chironomus it breaks up into drop-like 

 masses before the formation of the spindle. A similar metamorphosis 

 has been described by Blochmann in various Hymenoptera, but inter- 

 preted in a difi'erent way. 



(h) Testes. — The variations in the formation of the testes and in 

 the spermatogenesis are not so striking as in the development of 

 ovaries and ova. In all testes which arise from the differentiation of 

 the reproductive rudiment, cells with large nuclei are developed 

 internally, while round the wall of the tubule a sheath with small 

 nuclei is formed. From the former the sperm-follicle arises; the 

 nuclei divide, the outer form an epithelial layer, the inner grow and 

 divide ; the results form sperm-cells. 



(«) Comparison of Oogenesis and Spermatogenesis. — The testicular 

 tubules of insects with a terminal yolk-gland have, at the end of 

 larval life, exactly the form of ovarian tubules. The cells, which 

 represent yolk-cells in the ovarian tubules, become testicular follicles 

 in the testes. When the ova develope directly without yolk-glands, 

 the cells which, in the female, form ova, become sperm-follicles in 

 the male. When the ova arise in the terminal yolk-gland, the yolk, 

 or rather the male-cells in the female, remain undeveloped. The ova 

 arise from cells of another region ; the yolk-cells, i. e. the potential 

 male-cells, come to nothing and disappear. 



(j) Application to Classification. — Professor Schneider next con- 

 siders the relation of the development of the reproductive organs to 

 the general system of the Insecta. Neither this portion of his memoir, 

 however, nor the second special division in which the families are 

 discussed in detail, admit of short summary. 



Histogenesis in the Ovigerous Sheaths of Insects. — M. J. Perez* 

 finds that the young ovary of insects has all its cells identical ; that 

 these are indifferent at first, but give rise later to the follicular 

 epithelium on the one hand, and to the ovules and the vitellogenous 

 cells on the other. When there are no vitellogenous cells the ovules 

 result from the direct and successive transformation of some (the 

 axial) of the primitive cells ; those at the periphery and surrounding 

 the ovule proliferate, more or less actively, and arrange themselves 

 around the ovule, so as to form a follicular epithelium ; these are 

 always distinctly separated from the egg, and do not arise in its 

 protoplasm, as has been asserted by M. Sabatier and M. Wilm. 



* Comptes Eendus, cii. (1886) pp. 181-3. 



