12 Bulletin American Museum of Natural History [Vol. XLI1 



eating, the larva lifts its head out of the water and manipulates its food 

 by means of the mouth-parts. The labium and maxillae are used as 

 guides and to hold the prey while the mandibles macerate it. The legs 

 play no part in the handling of the food. Predigestion occurs and the 

 dissolved food is then drawn into the mouth by the suction of the 

 pharynx. 1 There is neither lock to the mouth nor tubes in the mandibles 

 such as are found in the dytiscid larva. This method of feeding refers 

 only to the aquatic larvae of the family and to Helophorus. I have not 

 observed the feeding of the other, terrestrial forms. According to 

 d'Orchymont, however, predigestion apparently does not take place in 

 them. 



There are usually two molts occurring during the larval period, 

 which lasts one or two months. Hydrobius 2 evidently proves an excep- 

 tion to the rule, as its larvse are found nearly full-grown in the early 

 spring and even then do not transform immediately. The typically 

 aquatic larva grows very rapidly and the first two instars take only 

 about a fortnight. Most of its life is, therefore, spent in the third or last 

 instar. 



When ready to pupate, the larvse leave the water and burrow in 

 moist earth, often under stones or sticks, where they mold a cell slightly 

 larger than the pupa to be formed. In the prescribed time (3-7 days) 

 the pupal skin is ruptured and the adult emerges soon after but usually 

 remains in the cell until fully colored. 



Explanation of Terms Used 



In order that the terms that are used in the technical descriptions 

 may be understood by the reader, a brief explanation of them is given 

 here and illustrations of typical structures are shown in Plate I. No 

 work has yet appeared in this country which deals with the difficult 

 structures of a campodeiform larva such as we find in this family. 

 Hopkins' paper on Dendroctonus has proved very useful, but the struc- 

 tures of that type of larva have not been compared with those of the 

 hydrophilid type. I have, therefore, used, for the most part, the terms 

 employed by European writers. D'Orchymont does not discuss the 

 various terminologies, except in regard to the stigmatic atrium. How- 

 ever, his labeled figures of the mouth-parts and his numerous notes aid 

 materially in giving one a clear understanding of his interpretation of 



JMethod described by Balfour-Browne, 1910. 



2 Miall reports hibernation in larvse of H. fuscipes and the author has observed it in H. globosus. 



