Benham. — Aquatic Larva of the Fly Ephydra. 311 



convex disc, which I believe forms the anterior end of the real 

 head, which is retracted, as has been observed to occur in Eristalis. 

 The mouth leads into a short cylindrical tube, which soon dilates 

 to form a pharynx, in the wall of which a number of sclerites 

 are present, the most conspicuous of which is essentially a ring, 

 with four backwardly directed processes, which no doubt serve 

 for the attachment of muscles. Though built up on the same 

 plan as that of Eristalis, it is very different in detail. 



Some of the puparia were merely empty skins, and these were 

 cleft horizontally on each side from the head backwards over 

 two or three segments : no doubt the fly had emerged by this 

 slit. 



In one case the skin was ruptured somewhere near the 

 middle of the body and exposed the pupa, which occupies only 

 a small portion of this internal cavity ; in length it extends 

 through about four segments, and in breadth is only half the 

 diameter of the puparium. 



We have, then, the whole series of stages in the life-history 

 of this creature, which I believe from the above - mentioned 

 references to be Ephydra, both from its habitat in salt pools 

 and from the resemblance in external form. Moreover, the genus 

 has already been recorded by Captain Hutton as occurring in 

 this country, for he described* E. aquaria from Christchurch, 

 which is 5 mm. in length, and this agrees with the length of the 

 pupa in the puparium above alluded to. 



No doubt the general history agrees pretty well with that of 

 Eristalis, and is as follows : The eggs are laid in the water of 

 salt marshy ground ; the larva?, issuing therefrom, burrow in 

 the mud, where the spinous covering and the specialised claws 

 serve as organs of locomotion, and the tail is directed upwards 

 to the surface for respiration : this probably occurs only at 

 intervals. The larva feeds on the organic matter in the mud, 

 and as the time for pupation approaches it seems that it uses 

 its hinder clawed segments 8 and 10 to cling to algse floating in 

 the water, for in nearly all the individuals I find threads of algse 

 held by these prominent segments ; and at this time the anterior 

 spiracles perhaps come into use. The skin now becomes hard 

 and dark-coloured. The tissues, as in other cases of similar 

 metamorphosis, become disintegrated, and later on become re- 

 arranged, if we may use the term, to give rise to the body of the 

 pupa. The larval skin has become a cocoon or " puparium," 

 and it seems likely that the imago escapes through the anterior 

 end — hence the object of the larva supporting itself by the algae, 

 so as to allow the anterior end to emerge from the water. 



* Trans. N.Z. Inst., vol. xxxiii., p. 90. 



