72 SUMMARY OF CURRENT RESEARCHES RELATING TO 



iusects differ greatly in tlie way in which the various kinds of cells are 

 formed from the indifferent elements. It is clear from their histological 

 peculiarities, and from the mode of origin of their elements, that the 

 ovarian tuhes which are of complex structure and are provided with 

 nutrient chamhers, must have been derived phylogenetically from tubes 

 without nutrient chambers. In some cases the nutrient cells are formed 

 at the same time and in the same way as the germinal cells, and they are 

 then to be regarded as germinal cells which have gradually lost the 

 function of forming ova and have taken on that of producing nutrient 

 substance. 



In the ovarian tubes which have several nutrient chambers the nutrient 

 cells may be formed at the same point as the egg-cells, and even later they 

 may be found mixed up with them at the commencement of the tube. The 

 tubes with a terminal nutrient chamber appear to have been formed owing 

 to the capacity for forming ova having been handed over from the primitive 

 germinal cells at the tip of the chamber to those which lie at its base. The 

 nutrient cells of other forms arose independently of the germinal cells, and 

 must not therefore be referred to them. In all forms the epithelium is 

 develojied in much the same way, and always has a great resemblance to 

 the indifferent elements of the terminal chamber from which it directly 

 arises ; the author was never able to convince himself of the formation of 

 epithelium from germinal vesicles, from the nuclei of nutrient cells, or from 

 the so-called ooblast-. Neither the ova of Hemiptera or any other insect 

 are formed of ooblasts, but arise, like the epithelial and nutrient cells, by 

 the gradual differentiation of the indifferent elements of the ovarian tubes. 

 All the various elements of the tube are morphologically of the value of 

 cells. 



Chemical Composition of Ova.* — Herr A. Tichomiroff has analysed 

 the ova of Bomhijx mori, and compared the composition before, and at the 

 close of incubation. The shell contains a substance which he terms chorio- 

 ninc, containing less sulphur than keratiue. The proportions of albumen 

 and insoluble salts, of aqueous extract and glycogen, of ethereal extract, 

 fat, lecithin, and cholesterine, of chorionine and chitin, of nitrogenous 

 bases, are noted. Before incubation the ova contain 100 parts of liquid 

 material and 35-5 of solid substances, while at the close of incubation 

 the respective figures are 88-8 and 30-2. In developing, the ova therefore 

 lose 7 per cent, of water and 3 per cent, of solid material. The loss is 

 principally in glycogen and fat. 



Law of Orientation of the Embryo in Insects.!— M. P. Hallez has 

 continued his observations on the relations which exist between the principal 

 axis of the mother and the organic axis of the egg, and between the organic 

 axis of the egg and the principal axis of the embryo. The insects best 

 adapted for such investigations are those which deposit their ova in cocoons, 

 those which have an oviscapt, or such as have certain peculiarities, such as 

 micropylar appendages 



The first form described is Lomsta viridissima, where it was found that 

 the head of the embryos is always formed at the superior part of the egg, 

 and that the convex line of the ovum corresponds to- the dorsal surface of 

 the embryo. 



In IIi/clrojMiis 2nceus the head, contrary to what obtains in most cases, 

 looks downwards ; the principal axis of the embryo has the same orienta- 



,,oL>^^^^^'^^^- ^- ^''ys'*^^- Cliimie, ix. (1885) pp. 518-32. Cf. Arch. Slav, de Biol., ii. 

 (Ibod) pp. 133-4. 



t Comptes Kendus, ciii. (1886) pp. G0(J-8. 



