ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 735 



to fix the animal at some depth among the water-plants, and so to 

 prevent its floating upwards. 



In the aerial forms we have first to notice those that move on the 

 surface of the water ; in these the legs are often provided with con- 

 siderable enlargements of the tracheal trunk, by means of which they 

 are enabled to float. Others have very long legs by which they can 

 balance themselves and extend over a large surface of the water ; the 

 lower surface of the tarsal joints, or that which is in contact with 

 the water, is provided Avith thick hairs. In some Diptera hairy lobes 

 are developed. Arrangements for climbing are very widely dis- 

 tributed, and are very various in character ; the most common are 

 hooks which by their sharp tips are able to enter the smallest 

 depressions and so obtain a firm hold ; sometimes they are cleft and 

 are thus adapted to hold on to fine branches ; sometimes they are 

 pectinate and enabled to catch hold of fine hairs. 



In very many cases there are organs of fixation ; in the locust 

 they have their chief mass made up of a largo number of free flexible 

 rods (not tubes). The periphery is occupied by scales which corre- 

 spond in number to the rods, with which they appear to be connected 

 by fibres ; the space between the rods is filled with a fluid. Below 

 these are groups of spindle-shaped cells which appear to be glandular 

 in character. The fixing surface of the Hymenoptera, Neuroptera, 

 and Lepidoptera consists of an unpaired lobule placed between the 

 hooks ; their structure is most complicated in the first-named order. 

 Observations on Vespa crabro did not result in the detection of any 

 space which could be regarded as a vacuum. The lower surface of 

 the lobule is soft and almost smooth ; a few short hairs may be 

 developed at its base ; below this is a hard chitinous mass with 

 stronger hairs. The upper surface is either covered with hairs or is 

 finely folded. Near the base is a chitinous plate carrying a pair of 

 strong setae. Within is an elastic bar which is rolled up in a con- 

 dition of repose ; when extended it brings the lobule into contact with 

 the surface on which the insect is standing. There are no well- 

 developed gland- eel Is. After descriptions of other modes of fixation 

 the author gives the following table. 



A. Organs of attachment at the end of the foot. 



a. Without fixing hairs Orthoptera. 



iForficula. 

 Coleoptera. 

 Sialis. 



B. Organs of attachment between the hooks. 

 a. A distinct median lobe. 



a. The median lobe with chitinous arches. 



1. Secondary in addition to the median lobe Neuroptera. 



2. No secondary lobes Hymenoptera. 



, ,T 1 ., • 1 I Lepidoptera. 



6. No chitinous arches wu- ? 



(i. No distinct median lobe. 



a. 'J'Ijo lobes hairy Diptera. 



h. The lobes not hairy lihynchota. 



