49 
these hooks erected by the muscles of the skin, the animal raises 
O. depresses h.mseif at pleasure, or turns about in the abscess and 
hnal y crawls out of it when ripe. The use of the terminal tcn- 
acula, observable m the Gastric species, would have been useless 
n this, as the oval form of the abscess retains them in then 
abode sufficiently secure. And by the motion of the larva in the 
abscess these hooks, by irritating thesurface of the sac, produce a 
discharge of pus for sustenance. 
In what manner the nourishment is received by this larva is 
not immediately discoverable. Indeed, it was not known to me 
i 1 an unexpected circumstance led me to its discovery; on im¬ 
mersing one of these larvrn in warm water with a view to rid it of 
pus and slime, I observed a considerable quantity of pus to 
e ejec ed from an aperture, which at other times was closed, 
this was at first considered to be the mouth; it, however, was 
ound on further research to be the real anus of the larva, for it is 
in the upper part of the larva, or that end which is applied to the 
external opening in the skin, (where may be also observed two 
small horny plates,) which are found on dissection to close the ex¬ 
tremities of the trunks of two large air vessels. Near to these plates 
an somewhat above them, this minute puncture is discernible. 
At other times, when closed, it was discernible with the utmost 
cu t,y. At fig. 3. is represented this aperture, a. together with 
the two horny plates, which close up the air vessels, being a view 
veiy considerably magnified, of this upper extremity of the 
larva. 
I rom a first view, this part would appear to be the head of the 
larva, being uppermost in the abscess; but as it is found to pro- 
duce the extremity of the abdomen in the future insect, it must, 
therefore, be considered as the tail; and the above-mentioned 
minute aperture is undoubtedly the anus, and is found to he in 
conformity to the same situation of the anus in others of this 
N 
