480 SIR J. LUBBOCK ON THE DEVELOPMENT 
larger, and contain the ends of the two lateral appendages, which towards the end of this 
period can be distinctly seen through the skin. 
The ovaries are two white cylindrical bodies, which occupy the whole length of the ab- 
domen. They consist of a great number of short egg-tubes, each of which is divided into 
two chambers (Plate LVIII. fig. 10). The upper chamber contains a number of vitel- 
logenous cells; it is elongated and more or less cylindrical in form, terminating at the 
upper end, as usual, in a delicate string. 
The lower chamber is elliptic, and contains numerous oil-globules, some of large size, 
It has a greenish hue, caused by the presence of numerous small globules. 
The Organs of Respiration. 
It has been already mentioned that the larv in the first three stages possess no respi- 
ratory organs whatever. This is a fact so exceptional that, so far as I am aware, no 
other case is on record. Even the youngest larvæ have hitherto been invariably 
found to possess tracheæ, and either spiracles or gills, as the case might be. We are 
apt to be surprised by anything which is unusual ; but in reality it appears more difficult 
to understand why these larvæ should not respire in the same manner as the Crustacea 
with wbich they live during the whole of their subaqueous existence, than why they 
should do so for a short part of it. 
Another unusual fact connected with the tracheæ of Chloëon is, that their internal chi- 
tinous envelope is not shed with the skin. In ordinary larvæ the inner skin of the 
tracheæ is shed at each moult, it being drawn out through the spiracles. "That the same 
is not the case in Chloëon depends evidently on the absence of spiracles, so that the 
shedding would be a physical impossibility. The necessity for a change ceases, however, 
with the possibility. Where there are open spiracles, dust, &c. must occasionally enter, 
in spite of the tufts of hair and other ingenious contrivances by which it is to a great 
extent excluded. At every change of skin, however, all foreign matters are necessarily 
carried away with the tracheal skin, and the passage is thereby kept free and V jor 
Where, on the other hand, as in the larva of Chloëon, there are no orifices, no foreign 
matters can possibly enter, and the necessity for changes of skin is perhaps thereby 
removed. 
When, however, the insect changes into the proimago and quits the water, spiracles 
are formed ; and at this moult, for the first time, the inner skin of the tracheæ is cast, 25 
is the case in other insects. 
Dr. Hagen has recently published a posthumous memoir by Prof. Rathke *, a transla- 
on of which has appeared in the ‘Annals and Magazine of Natural History’ (ser. 3. vol. ix) 
In this paper Prof. Rathke expresses opinions, as to the manner in which the respira- 
tion of inseets is carried on, which are very opposite to those which I have advocated in 
my memoir “ On the Tracheæ of Insects," published in the Transactions of this Society 
for 1860. 
Dr. Rathke, after describing the so-called respiratory movements of insects, discuss? 
the function which they perform. | 
* Schriften der Königl. 
ti 
physik-ükonom. Gesellschaft zu Königsberg, 1861, p. 99. 
