RECENT LITERATURE. 233 



stroke of the large autennte was as nearly as possible identical in all 

 the specimens examined. Two accidents, however, led to an inklinc 

 of the truth. In one case a Daphnia, who had some sealing-wax 

 cement (used in an unsuccessful experiment) left attached to the'^head, 

 was observed to have a tendency to swim somewhat obliquely back 

 downwards, thus imitating the normal progression of a Simocephahis. 

 In the other, an air-bubble had penetrated the brood cavity of a Simo- 

 cephaJus in consequence of the latter having been left too long upon a 

 glass slip without water. The swimming of the creature " was most 

 curious. It struggled hard against the upward pull of the air-bubble, 

 and by the vigorous use of its antennae it managed to make some pro- 

 gress in an obliquely downward direction ; but it was no longer swim- 

 ming in the manner of a Simocephalus, but . . . with its back^'upwards. 

 It also clung to the sides of the glass in an inverted position, which is 

 just the opposite to the normal behaviour of animals of the "enus. 

 The two cases of abnormal swimming just alluded to, taken in con- 

 nection with what has been already found out about the direction of 

 the stroke, proved conclusively that the main factor in determining the 

 positions of the animals when swimming freely must be the situation 

 of the centre of gravity." In fact, the position of the animal is due 

 to the net result of gravity and the direction of the stroke (of the 

 antennae), modified by the speed of the progress, and also by the 

 possession of shell-spines, the most active swimmers — the clear-water 

 forms — having the greatest development of the shell-spine (and even 

 the possession of a head-spine) ; while D. pulex and others, which are 

 normally comparatively sluggish, exhibit short shell- spines. 



The paper is illustrated by diagrams showing the directions of the 

 various forces. .., „^ „ 



(t. W. K. 



E, P. Felt. Sixteenth Report Injurious and other Insects. (1901, 

 Bull. Soc. N. Y. State Mus. vol. vii. No. 36, pp. 949-1068 ; two 

 coloured and thirteen plain plates (comprising twenty- three 

 photographs), one plan, and two text figures.) 



The New York State Reports have always held a very high place 

 among contributions to economic entomology, though under the care 

 of Dr. Felt their general plan and detailed execution show an im- 

 provement even upon the old series. The principal feature of the 

 Sixteenth Report is the record of experimental work with insecticides 

 in fighting scale-insects, especially Aspkliotus perniciosiis, Comst. This 

 is elucidated by a large plan of an infested orchard, and twenty photo- 

 graphs of infested trees, &c. Two beautifully executed coloured plates 

 illustrate accounts of the gypsy moth {Porthetria dispar), and the 

 "Palmer-worm " (the caterpillar of a Gelechiid, Ypsolophiis poDietellus, 

 Harris). The relaxation of the efforts of the Massachusetts Common- 

 wealth towards the extermination of the gypsy moth leads to the fear 

 that it is only a question of time before its destructive powers will be 

 felt in New York State. One of the most remarkable photographs is 

 plate 16, showing forest-tent caterpillars (Clisiocampa disstria) clustered 

 on a tree-trunk. P tt- t- 



