50 BULLETIN OF THE BUREAU OF FISHERIES. 



these conditions for several weeks with very few fatalities, even though the water ceased 

 dripping several times for a number of hours, thus causing a considerable drying out. 

 The pupa, which seem never to have been found in nature, were observed to be located 

 in a fold in the pocket where the water supply was more uniform and where greater 

 security of position was doubtless possible. 



The author was unable to find a pupa out of doors even after he had bred the pupae 

 in an artificial environment. The larvae, while quite abundant in the one habitat in 

 which the author succeeded in finding them, either do not live to transform to pupae in 

 any considerable numbers or else they possess some unusual habits which entirely escaped 

 the writer's notice, for repeated search for pupae in the most likely places and at such 

 widely separated intervals was made that it does not seem possible that they could have 

 been abundant in the environment occupied by the larvae. That the pupa can live under 

 the same conditions in which the larvae are found is amply demonstrated by the author's 

 laboratory experiments, where upwards of 50 per cent of the nearly mature larvae trans- 

 formed to adults. Another source of information which seems to corroborate the notion 

 that the pupae are not abundant was the fact that repeated sweeping over these rocks 

 and in the adjoining region failed to give even a single adult specimen. The eggs so 

 far as is known have never been found, and nothing is known of the mating habits of 

 the adults. 



FEEDING HABITS. 



The feeding habits of Orphnephila are no less unique than its other environmental 

 adaptations. Let us first take up the structure and arrangement of the mouth parts, 

 as a knowledge of their nature and position is fundamental to all ecological considerations. 



Thienemann (1909), as mentioned above, has figured the more commonly observed 

 mouth parts of Orphnephila, but the separate drawings give no adequate notion of the 

 relative position of each part. The author has found it necessary to draw the mouth 

 parts as they appear in position and then for the sake of comparison several of them 

 separately. The assembled mouth parts (figs. 53 and 54) show that the mandibles, 

 instead of moving from the outside inward toward the mid line, as described in the case 

 of the chironomids, are so hinged as to move outward from the mid line when in use for 

 the purpose of scraping food from the rocks. This arrangement of the mandibles in 

 Orphnephila, so far as the author is aware, is unique among Arthropoda. Correlated 

 with the mandibles are the maxillae which are furnished with a border of spoon-shaped 

 plates which are opposable to the mandibles. This arrangement makes their function 

 as collecting baskets, for gathering in the particles scraped free from the stones by the 

 mandibles, quite obvious. The rods shown in figure 54, rd are supporting structures which 

 fuse with the clypeal plate and extending beneath the mandibles form a partial support 

 for the articulation of the maxillae. The very marked development of the labrum 

 suggests at least its probable function, and while the writer has not been able to observe 

 this particular mouth part in use it is probably brought into play in connection with the 

 mandibles in such a way as to scrape an intermediate area not touched by them. 



The rather narrow labrum is provided with a considerable number and variety of 

 spines at its terminal end and, together with the somewhat similarly clothed hypopharynx, 

 is doubtless instrumental in collecting the food scraped loose by the labrum, as well as 

 in the removal of the food particles assembled by the maxillae {fig. 5j, lb). 



