with some Remarks on the Nature of the Spongiæ Marine. 391 
ing within the cells or canals of this kind of Sponge, is one, I believe, at pre- 
sent unknown, and one of a very remarkable form and character, It is in 
appearance not unlike a wingless Aphis; it varies somewhat in size, probably 
according to its age; is apterous and of a green colour, much resembling that 
of the Sponge itself, but is occasionally rather more marked with brown. It 
seems to inhabit this Freshwater Sponge alone, for I do not recollect to bave 
noticed it in any other production ; it burrows in it, feeds upon it, eating away 
large pieces of it; coming forth from its hole, it is often seen walking over 
the surface of the mass, and retreats, particularly when disturbed, within the 
canals again. Possessing on the under part of its body certain membranaceous 
appendages, which are clearly a sort of branchiz or gills, it makes use of them 
for the purpose of breathing. Whilst it effects the function of respiration the 
insect remains within its hole perfectly still, but only keeps rapidly vibrating 
these gills or branchial appendages, by means of which currents are produced 
in the water near to the spot where it is lodged. 
To this insect, then, I attribute for the most part those currents which I 
have observed flowing into, and out from, the pores or canals of the Spongilla 
fluviatilis; or else to the same cause, namely, to the process of respiration 
being carried on by some molluscan, or insect, hid within and inhabiting that 
individual specimen; for I have always succeeded in discovering, whenever I 
have noticed similar currents or streams in the water, the presence either of 
some parasitical insect, or of some molluscan, upon which the Sponge has 
grown and afterwards entirely invested. Moreover, I have never yet been 
able to perceive these currents in any living mass of this Freshwater Sponge 
Sponge insects are aquatic and furnished with gills, which no imago that I am acquainted with pos: 
sesses. If regarded as larve, it is difficult to conceive even to what order of insects they belong, the 
structure of the mouth being unlike every group having aquatic larve ; in some respects they are al- 
lied to the larvæ of the Hemerobii, which have long mandibles and maxillæ, but these are all terres- 
trial. We are too well acquainted also with the larvae of the Trichoptera to regard them as belonging 
to that order ; and in the Neuroptera we know the transformations of all the groups. "There is, how- 
ever one anomalous genus, Acentropus, of which even the order is doubtful; and as we are ignorant 
of its early stages, it may possibly belong to that.” 
Having kept in a basin of fresh water for many days together specimens of the Spongilla wherein 
were some of these insects, and having never observed them even beginning to transform, I am very 
much inclined to consider that they have attained their perfect state. A short notice of this insect is 
given in the Mag. Nat. Hist., vol. iii. N. S. p. 200, No. for April, 1839, 
VOL. XVIII. 3 F 
