ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 405 



different forms, and formulates the following conclusions, (a) Diurnal 

 winged insects, Hymenoptera, Diptera, and Lepidoptera, when blinded 

 by covering the entire eyes with black, or by cutting all the optic nerves, 

 rise to a great height in the air when liberated, (b) When the compound 

 eyes are suppressed, but the frontal ocelli left, in Hymenoptera, Odonati, 

 and Diptera, the insects behave exactly as if the ocelli also had been sup- 

 pressed. When freed, they rise vertically as before. In a chamber 

 lighted from one side they behaved as if tbey were totally blind, (c) 

 But if the frontal ocelli be alone suppressed, the above insects behave as 

 if they had lost nothing, (rf) In diurnal insects equipped with com- 

 pound eyes, the ocelli count for almost nothing. They only afford the 

 animals very feeble perceptions which they do not know how to use. 



The author concludes his memoir with the following suggestions, 

 which he describes as " plausible hypotheses," supported by a certain 

 number of observed facts : — (1) Diurnal insects, in which all the eyes 

 have been suppressed, still enjoy dermatoptic perceptions. (2) They 

 are almost reduced to the same limitations if the ocelli alone are left at 

 tbeir disposal. (3) The dermatoptic perceptions are the primary cause 

 of the ascending flight of liberated blinded insects. (4) The frontal 

 ocelli serve neither for the perception of movements in adjacent objects, 

 nor for the perception of light in relatively obscure media. (5) The 

 simple eyes, which the author has shown to function in an imperfect 

 fashion in most Myriopods, in many Arachnids, and in caterpillars, have 

 entirely lost their utility in the great majority of insects equipped with 

 compound eyes. 



Secretion of Pure Aqueous Formic Acid by Lepidopterous Larvae 

 for the Purposes of Defence.* — Mr. E. B. Poulton has made observations 

 on the larvae of the genus Centra (Dicranura), which have long been 

 known to have the power of ejecting a colourless fluid from the mouth of 

 a gland which opens on the prothoracic segment. This secretion was 

 found to contain about 33 per cent, of anhydrous acid. A mature larva, 

 which has not been previously irritated, will eject 0*050 grm. of secre- 

 tion, containing about 40 per cent, of acid. It appears certain, from 

 the chemical investigations that were made., that the secretion consists 

 of a strong aqueous solution of very nearly pure formic acid. The rate 

 of secretion is comparatively slow ; starvation lessens its amount, and 

 decreases the quantity of the acid., but this seems to be due rather to the 

 general health than to the acid being formed directly from the food ; 

 there was no difference when the larvae fed on poplar and not willow, or 

 vice versa. 



Finer Structure of Butterfly Scales.f — Mr. T. F. Smith regards the 

 scales of Amatlmsia as being very simple in structure ; longitudinal ribs 

 run " from end to end of the scale ; cross-ribs at regular intervals, and 

 rising from these two or three beads, some of which seem to stand close 

 on the cross-ribs, and some to rise from them with a stalk." In Morpho 

 tnenclaus attention should be given to the contrast between the coarseness 

 of the main structure, and the beautiful minute beads with which it is 

 outlined. In Papilio memnon " instead of a single cross-bar at regular 

 intervals connecting the long ones, they are connected by a beautiful 

 interlacing pattern, from which rise numerous minute filaments not more 



* Rep. Brit. Assoc. Adv. Sci., 1887 (1888) pp. 765-6. 

 t Journ. Quekott Micr. Club, iii. (1887) pp. 178-81. 



