ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 801 



medullary mass is invested by unipolar cells which send out prolonga- 

 tions to it, and these are grouped into four separate lobes. 



The optic nerve is formed of two bundles which are perfectly 

 distinct, and have each different origins and terminations ; the superior 

 arises from the posterior surface of the posterior capsule and passes to 

 the anterior and superior region of the brain, where it penetrates into 

 the masses of dotted substance, not, as M. Beyer thought, stopping 

 at the cerebral cortex ; the lower part of the nerve is much the larger ; 

 it arises from the inner edge of the three capsules of the medullary 

 mass, and penetrates the lower and lateral portion of the brain. 



Nature of the Colouring of Phytophagous Larvae.* — Mr. E. B. 

 Poulton has made some experiments on the relation between the 

 colour of phytophagous larvee and that of their food-plants. He comes 

 to the conclusion that the influence of the plant is not uniform, that it 

 must act during a large proportion of the whole larval life if it is to pro- 

 duce an effect, and that effects of surface-coloration due to consistence 

 may be imitated in colour ; he thinks it extremely probable that the 

 effects accumulate during successive generations. These effects are 

 partially due to the pigment which is proper to the larva and has no 

 immediate relation to the food-plant ; more complicated changes ob- 

 tain with the derived pigments, and these are due to the predominance 

 of one or other of the vegetal colouring matters in the tissues and 

 blood, and before this in the materials which traverse the walls of the 

 digestive tract. 



The effects observed cannot be explained by the simple theory of 

 phytophagic influence, and Mr. Poulton thinks the term should be 

 abandoned so far ; it only holds good for the broad fact that pigments 

 derived from the food-plant play a most important part in larval 

 coloration, and provide the material which is moulded by some subtler 

 influence into a likeness to a special part of the environment. No- 

 thing can be said as to this influence save that there are indications 

 of a nervous circle whose efferent effects are seen in the regulation of 

 the passage of pigments through the digestive tract into the blood, 

 and thence to the tissues, and in the colour of a certain amount of 

 true larval pigment ; the efferent part of the circuit must originate in 

 some surface capable of responding to delicate shades of difference in 

 the colour of the part of the environment imitated. These facts offer 

 some difficulties ; tbey arc the gradual working of the process, often 

 incomplete in a single life, the excessively complex and diverse result, 

 and the special character of the pigment. 



Variations in tlie colour of the derived pigments in the blood 

 occur in some opaque forms, and it is possible that the variation be- 

 gan in this way, and was afterwards rendered efficacious by co-ordina- 

 tion with the environment. 



How Insects adhere to flat vertical Surfaces.! — Hcrr H. Dcwitz 

 gives an account of some furtlicr observations on this subject, tending 

 to prove that the secretion by which, o. g. flies adhere to window 

 panes is not a thin fluid of a fatty nature, but much more consistent. 



• Prf)c. Roy. Soc., xxxvlii. (1885) pp. 2(J9-315 (1 chart), 

 t ZwI. Anzeig., viii. {188.'i) pj). l.')7-9. 



