THE society's NOTE-BOOKS. 155 



EXPLANATION OF PLATE XV. 



Upper Half. 

 Fig. 1. — Velia currens. 

 ,, 2 and 6. — Antennae of Velia and Gerris. 

 ,, 3 and 5. — Tarsi of ditto. 



,, 4. — Tarsus showing the ungues situated in a cleft of the terminal 

 joint. 



Daphnia. — When examining these rapidly-swimming little 

 creatures in the living state, if you put them into a cell where they 

 have room to swim about, it is impossible to get a view^ of them for 

 many seconds together ; while, on the other hand, if you put them 

 on a flat shde^ a very slight pressure applied to the covering-glass 

 is sufficient to squeeze out their interior. The best way of seeing 

 them is to place the drop of water containing them on a flat slip ; 

 drop on it a few loose fibres of cotton wool, and then put on the 

 cover ; they are thus held entangled in the fibres, as in the meshes 

 of a net, and may be watched at leisure. 



H. F. Parsons. 



The eggs in this genus are not carried in external sacs, 

 as in Cyclops, but are lodged in the back, under the shell ; in 

 which receptacle the young are hatched, and are there retained 

 until the moulting of the shell. The eggs produced in the 

 autumn are snugly embedded in a thickened part of the carapace, 

 called the ephippium ; in w^hich, after it has been cast off from the 

 animal, they remain until they are hatched. By carefully focus- 

 sing, the opening in the under-side of the shell, through which the 

 legs are protruded when swimming, may be seen under the 

 microscope. 



R. A. Hankey. 



Thymus gland. — The Thymus is a body w^hich fills a large 

 portion of the anterior part of the thorax in young mammalian 

 animals. After birth it dwindles away, and disappears by the 

 time adult-life is reached. In the calf it is called the " Sweet- 

 bread ; but the sweetbread of the pig is the pancreas, a very 

 different organ. The Thymus is one of the ductless or blood- 

 vascular glands ; its use is not known, but is supposed to be to 

 modify in some way the blood which passes through it, or the 

 lymph. It has a capsule of connective tissue, which sends in 



