390 Mr. Hoac's Observations on the Spongilla fluviatilis, 
first called to them by seeing some little extraneous substances floating in the 
water and being carried by the stream setting in directly to a particular part 
of the Sponge. With a good magnifier I then clearly perceived not only this 
current in action, but likewise another flowing from the canals through their 
large orifices or oscules, and bearing along with it small ejectamenta or 
brownish bits of the Sponge or of soil, which I frequently observed turning 
over and over, and sometimes kept by the currents in a revolving motion within 
the oscules, and thereby undoubtedly showing that certain flowings or streams 
were taking place in the water. I have further established the presence of 
them by putting a fresh specimen of the Spongilla fluviatilis in a dish of 
water and sprinkling a little calcined magnesia on the surface; this powder 
soon exhibited motions, and betrayed by its being carried round and round 
upon the water in different directions, that strong and distinct currents were 
actively going on. After many minute examinations in endeavouring to solve 
the cause of these phzenomena, I have hitherto invariably found a worm or an 
insect, or some crustaceous or molluscous animal, concealed within the Sponge, 
and by which the currents were actually produced. 
A parasitical insect*, indeed, which I have seldom failed to observe lurk- 
* Mr. Westwood, F.L.S., having more fully described this curious insect in a letter dated Novem- 
ber 30th, 1838, with which he kindly favoured me, I will add the following interesting account from 
it: “ The insects you have sent me are as anomalous as the production they inhabit. From their 
small size, soft texture, six long legs, and green colour, they have much the appearance of small 
wingless Aphides; but this is only in appearance. On examining them under a lens, they are seen 
to be 13-jointed, of an elongated oval form, clothed at the sides, and especially at the extremity of 
the body, with very long sete, which are also found sparingly upon the legs, The latter organs are 
not those of a perfectly organized imago, for they resemble those of the immature Coccide, or rather 
the legs of the larvæ of the Hemerobii, &c. The antennæ are nearly half the length of the body, 
joint, and apparently very indistinctly articulated. The 
sete, as long as the antennæ, between which they are 
distance apart. The underside of the body, or at least 
with elongated, flattened, membranous appendages ; 
ic Neuropterous and Trichopterous larvæ, are evidently 
false gills, and employed in respiration. From the characters, and with the materials I now possess, 
it is impossible to decide upon the real nature of these little animals: neither is it possible to decide 
whether they are in the nues or imago state. There are some imagines amongst the Aphide, Coccide, 
and some other groups, which never gain wings, but always retain their larvalike form; and in the 
Coccide we have a mouth composed of four elongated sete, as I have discovered; but then these 
