C 
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Life-history of Phalacrocera replicata. oo 
~ 
interpretation throw light upon the disappearance of the 
cords in the pupa, or upon the resemblance of the cords 
to the stalked prominences found elsewhere in the 
heematoccel, and to the cenocytes. It seems to us much 
more probable that all the structures described yield 
corpuscles, filaments, or other living nutritive particles, 
which are discharged into the blood at a time when the 
rapid growth of new tissues calls for enrichment of the 
fluid. 
In the cellular cords we have a mass of epidermic 
reserve-tissue, which projects far into the hzmatoccel, 
and into that part of it which becomes specialized as the 
heart. This is one more instance of that tendency of 
epiblastic and hypoblastic tissues te bulge into any inter- 
vening space, which has led to so much perplexity in the 
interpretation of so-called mesoblastic organs. 
We have considered the possibility that the cellular 
cords may be an organ of internal secretion. There is 
no positive evidence known to us which points to any 
such conclusion, and the rapid disappearance of the cords 
during the pupal stage seems to tell strongly against it. 
4. The respiratory organs of the larva, 
There is one pair of spiracles, situated on the dorsal 
surface of the last segment, between the base of the 
dorsal process and the anal hooks. ‘The larva is there- 
fore metapneustic, aS is nearly always the case with 
Tipulidee. The skin about the spiracles can be retracted 
so as to form a deep recess, with which both spiracles 
communicate. ‘The spiracle forms the outer end of an 
air-chamber, 1uto whose cavity strong and close-set sete 
project. Towards the surface the sete become rod-like, 
and their inuer ends are attached to acentral plug. The 
structure is much the same as in the larva of Dicranota,* 
and in neither case have inlets for the air been discovered. 
In both larvae, however, the spiracle is exposed at times 
to the air, and the trachez are filled with air. ‘The 
renewal of the air seems to take place at night, when 
both Phalacrocera and Dicranota have been seen to push 
their spiracles out of the water. There are two main 
tracheal trunks, which run along the dorsal surface and 
give off branches. In most of the segments there is a 
* Miall, Trans. Ent. Soc. Lond. 1893. 
