390 PHILOSOPHICAL TRANSACTIONS. [anNO I767, 



it, or to the increased celerity of the blood, certainly must have heated to a very 

 great degree, 



VII. Of a very Remarkable Aqtiatic Insect,* found in a Ditch of standing Water 

 near Norwich, in the Spring of 1762. By Edivard King, Esq., F. R. S. p. 72. 



Plate 10, fig. A is the female, and b the male, both represented on their 

 backs, in the posture in which they usually swim; a, a, are a number of smal 

 transparent, fringed, fins, placed parallel, and contiguous to each other. They 

 are almost always in a waving motion, and the animalcules seem to keep them- 

 selves suspended at different heights in the water, by means of them ; for on 

 their ceasing to move they sink to the bottom : d is one of those fins belonging 

 to the female seen in front, and h is one of those belonging to the male, in 

 which there is a very remarkable difference: c is the head of the female; and g 

 the head of the male; distinguished by three projecting substances like horns 

 or tusks, which are marked k in figure b ; one of the long ones on the side is 

 drawn separate at e, and the crooked one in the middle at f ; this last probably 

 serves as a kind of trunk, and the former may be of service to catch their prey, 

 whatever it is; i is a very singular projecting substance in the male, and may 

 perhaps contain the parts of generation ; and b is the ovarium of the female, in 

 which, it being quite transparent, the ova or spawn are very visible, and may be 

 seen from time to time to change their places, and to have a kind of circulation. 



c is a view of the female, placed on its back, in order to show the position of 

 the fins, and their appearance when one looks down upon the insect ; and d is 

 the male, placed with its back uppermost, in the posture in which he some- 

 times lies still at the bottom of the water. Lastly, b is the tail magnified in a 

 microscope, showing the hairs which grow on both sides out of it; but as the 

 animalcule did not lie still long enough in the water, he could not view it with 

 a glass so exactly as he wished to do, and therefbre is not sure of the accuracy of 

 the drawing of this part ; all the other parts he has drawn as carefully as he was 

 able, and they are about the natural size. 



In these insects, besides their form, several particulars are very remarkable 

 1 . Their bodies are entirely transparent, and mostly of a yellowish hue, except 

 towards the tail, and part of the ovarium, where the colour is reddish ; and, 

 through a long vessel, which reaches almost the whole way from the head to 

 the tail, somewhat of a circulation, by fits and starts, is very visible, even to the 

 naked eye. 2. In the ovarium of the female, the ova, which are of a mixai 

 colour in different parts, some brown, some yellow, and some red, are also in a 



* The elegant animal here described is the Cancer Stagnalis of Linnaeus. It has been amply de- 

 scribed by Schoefter and others. See vol. i. of the Transactions of the Liniwean Society, p. 103. 



