ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 379 



imagines of Diptera, Orthoptera, Forficulidse and Lepisma ; it is smaller in 

 the Coleoptera and Neuroptera, and is wanting in other insects. At the 

 hinder end of the foregut of many insects the cuticle forms a fold which 

 extends as far as the anus in the form of a tube. Professor Schneider 

 proposes to call it the infundibulum. It is generally present in all the 

 forms that have a proboscis, but is wanting in the Dytiscidse and Carabid83 

 among the Coleoptera, and is found in all larvae except those of Lepido- 

 ptera. All the insects and larvse that possess it eat hard and even indiges- 

 tible foods, while the others take fluid nutriment. When it is present in the 

 larva it may persist in the imago even when, as in the Diptera, the mouth- 

 organs and the mode of life are altered. Where it is found, the materials taken 

 into the intestine do not touch the surface of the mid- or hindgut. The 

 enteric respiration which obtains in many insects has no effect on the con- 

 tents of the intestine, as the infundibulum is elastic and firmly incloses the 

 contents. This structure was first seen by Wagner in the viviparous larvae 

 of the Cecidomyise, where alone it has till now been noticed. 



Comparative Morphology of the Brain in Insects and Crustacea.* — 

 M. H. Viallanes gives the names protocerehrum, deuto-, and trito-cerehrum to 

 the three lobes of the supra-oesophageal ganglion of the decapod Crustacea. 

 He compares each lobe, which consists of two lateral halves connected 

 across the middle line, to a ganglion of the ventral chain ; although the 

 trito-cerebrum appears not to be so connected. But from an examination of 

 these parts in some of the Orthoptera, he finds a commissure between these 

 lobes passing below the oesophagus. The protocerebrum innervates the eyes 

 in both Crustacea and Insects ; the deutocerebrum innervates the antennae 

 of insects, and the antennules of Crustacea, and the nerve rises in two roots ; 

 in both classes a nerve passes from this lobe to the integument ; the tritocere- 

 brum sends nerves to the second antennae in Crustacea, and to the labrum in 

 Insects : hence he draws an homology between these structures ; and con- 

 cludes that there are three prebuccal segments in both classes. 



o. Insecta. 



Vision of Insects.t — M. A. Forel gives an account of past and recent 

 experiments on the vision of insects, and sums up the conclusions as 

 follows : — 



(1) Insects direct themselves, in flight almost wholly, and on the ground 

 partially by means of their facetted eyes. The antennae and buccal sensory 

 organs cannot serve for directing flight. Their extirpation makes no 

 difference. 



(2) J. Miiller's mosaic theory is alone true. The retinulae of the 

 compound eyes do not each receive an image, but each receives a simple 

 ray more or less distinct in origin from that of its neighbours. Gottsche's 

 theory is false. (Miiller, Grenacher, Exner.) 



(3) The greater the number of facets, the more elongated the crystalline 

 cones, the more distinct and the longer the vision. (Miiller and Exner.) 



(4) Insects can see particularly well the movements of bodies, and 

 better during flight than when at rest, the image being displaced in relation 

 to the eye (Exner). This perception of the mobility of objects diminishes 

 as the distance increases. 



(5) Contour and form are only indistinctly appreciated, and the more 

 indistinctly the fewer the facets, the shorter the crystallines, the farther 



* Comptes Eendus, civ. (1887) pp. 444-7. 



t Rec. Zool. Suisse, iv. (1886) pp. 1-50 (1 pi.). - 



2 C 2 



