TRANSACTIONS OF THE LINNEAN SOCIETY. 139 
that the tube is not a simple one, but that the interior is 
formed by an internal tube, formed of a distended uterus, 
coequal in size with the calibre of the integuments throughout 
nearly the entire length of the worm, but terminating at 
either end in a slender prolongation, which he regards as the 
ovaries. Like previous observers, he has been unable to 
detect any external genital opening. He further shows that 
the slender intestinal tube runs down between the wall of 
this distended uterus and that of the body. 
He then goes on to describe the structure of the young 
Filariz, and traces their development from the earliest stages. 
In these he has noticed two peculiar organs situated at the 
junction of the anterior three fifths with the posterior two 
fifths, and which seem to have altogether escaped the notice 
of previous observers. They consist of two minute, globular 
sacculi, embedded in the substance of the body behind the 
anal opening, and communicating with the exterior by 
narrow, short canals. Their nature is obscure, unless they 
represent the rudiment of a water-vascular system. 
V. Our space will hardly allow us to do more than men- 
tion the title of a second communication from Mr. Lubbock, 
‘On two Aquatic Hymenoptera, one of which uses its wings 
in Swimming.” 
“ On one of the early days in August,” he says, “I was 
enjoying myself by watching the animals in a basin of pond- 
water. It is customary to regard the inhabitants of fresh 
water as less beautiful and varied than those of the sea. But 
though our inland lakes and rivers can boast no _ sea- 
anemones, no star-fishes, Medusz, shrimps, nor sea-urchins, 
they are still full of beauty and variety. Without counting 
the rarer forms, almost every weedy pool contains specimens 
of Daphnia, Cyclops, Diaptomus, and Asellus (and he might 
have added Branchipus), among Crustacea; the Hydra among 
Polypes; the lovely green Volvov, and many other Algz, 
besides numerous Desmidize and Diatomacee; with insects 
almost innumerable. Besides the perfect insects, such as 
water-beetles, Notonecta, Nepa, and other Hemiptera, there 
are larvee of dragon-flies, beetles, Phryganeas and Ephemeras, 
the beautifully transparent larve of Corethra, and many other 
species of Diptera. But though most of the great orders are 
more or less richly represented, no aquatic species of Hymen- 
optera or Orthoptera had till now been discovered.” * * 
“‘ Great, therefore, was my astonishment on the occasion 
to which I allude, when I saw in the water a small, Hymen- 
opterous insect, evidently quite at its ease, and actually 
swimming by means of its wings. At first I could hardly 
