ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 429 



nating silkworm ova may retain their vitality, that is, their power of 

 further development, though kept for long (152 clays) in conditions 

 where respiration is impossible (in CO2). The various objections of 

 Prof. Verson are answered in detail, and the conclusiveness of the 

 experiments is emphatically defended. 



Colour-relation between larva of Smerinthus ocellatus and its 

 Food-plants.* — Mr. E. B. Poulton gives an account of his investiga- 

 tions on this subject. 



Numerous experiments were undertaken by him with larvae cap- 

 tured and with larvfe hatched from five batches of eggs : these were 

 placed, some on one food-plant, others on various other food-plants, and 

 the colour of the larvfe was found to vary according to the colour of 

 the leaves upon which the larvae rested. The author concludes from 

 these experiments that the colour of the larvae of Smerinthus ocellatus is 

 determined (1) by hereditary influence ; (2) by the colour of the leaf 

 upon which it lives, and not by the substance of the leaf when eaten ; 

 (3) by individual variation with similarity of parentage, &c., and 

 conditions. In this way the author found that the larva maintains a 

 colour-relation with the food-plant upon which it is hatched, adjustable 

 within the limits of a single life. He points out that this differs from 

 the usual resources in the scheme of larval protection, by resemblance to 

 environment ; for whereas, in most cases, natural selection has finally 

 produced such a resemblance, which is common to all the food-plants 

 of the larva ; in this case the same process has given to the larva a 

 power which enables it to answer, with corresponding colours, the 

 difference which obtains between its food-plants. In the case of 

 Amphibia, fish, &c., the change is due to the environment acting as a 

 stimulus on the nervous system ; whilst in the case under considera- 

 tion the change is due to the absorption and product of pigments, 

 rather than modification of them, when already formed. 



Embryology of Muscidse.f — Prof. A. Kowalevsky communicates 

 the results of his investigations, begun many years ago (1873), of the 

 development of Muse idee. 



(a) The segmentation begins about an horn* after the egg is laid ; 

 the first two nuclei lie near the pointed anterior pole ; the segmenta- 

 tion masses at first lie in the centre, but as they increase in number 

 move outwards to the perij^hery. Posteriorly, the pole-cells penetrate 

 outwards into the space between the ovum and the vitelline membrane. 

 The others, which exhibit a club-like form, with the pointed end 

 inwards, pass out, dividing as they go, to form the blastoderm-cells, 

 incorporating in so doing part of the peripheral plasma. Some nuclei 

 remain in the interior, forming the yolk-cells. (6) The groove appears 

 at first ventrally, from the head-end backwards, extending thence over 

 a third of the dorsal surface. The closure also occurs from before 

 backwards, (c) The emhryonic membranes are characteristic only in 

 this (as Graber has noted) that they cover only a small portion of the 

 embryonic tract, viz. the dorsal portion, and that they subsequently 



* Proc, Roy. Soc., xl. (1886). See Nature, xsxiii. (1886) pp. 474-6. 

 t Biol. Centralbl., vi. (1886) pp. 49-54. 



