436 



iu which the forms are named. Limnodrilus is eaten voraciously by the 

 AmMiistoma larvse and by Diemyctylus. Diemyctylus has been observed a 

 few times to take SlmocepItaJus. 



The insects that accidentally fall into tJie pond are captured bj' the 

 Gyrinidse and Hygrotrechns. 



The Corethra larvpe feed on ostracoda and possibly other forms in this 

 pond. Miall ('95, page 115) says, "Corethra lan^se feed upon small aquatic 

 animals such as Ephemera-larvse, Daphnia, or Cypris." The Hydrophylidte 

 feed on the decaying organic matter. The Dytiscidse have not been observed 

 feeding in this pond, although they are known to be carniverous, Kellogg 

 ('04, p. 258). The larvae of the Anura of this pond are rather omniverous. 

 They eat filamentous algfe, desmids, diatoms, protozoa, ostracoda and de- 

 caying organic material. There seems to be very little if any discrimina- 

 tion in the selection of food. Not all of the material eaten contributes to 

 the nutrition of these larvge. The rate of digestion in cold blooded verte- 

 brates has been shown by Riddle ('09) to vary directly mth temperature. 

 However, at ordinary temperatures many organisms pass through their 

 alimentary tracts unchanged. In the laeces of iarvre placed in tap water, 

 Oedoffonium, Closterium and DocGidium are common. From the alimentary 

 tracts of larvae kept for 5 days in w^ater, which had been previously' boiled, 

 have been taken Euglena, Pliacus, Spirogyra, Oedogonium, Closterium, 

 Doccidimn. The filamentous algae and Gloaterium were in part disinte- 

 gi'ated. The Euglence were very active. In another series that was kept 

 10 days, Ostracoda (Candona?) were found alive in the large intestine of 

 six specimens. These facts indicate that the nutrition is derived from 

 dead organic matter (filamentous alg;e and Closterium) and that the in- 

 clusion of other, living organisms is accidental. 



In connection with food relations may be mentioned the mechanical 

 comminution of plant debris. When plants die in the pond, they stand foi 

 a time, then fall on the surface of the water where they float for a while 

 and then sink. During this period they are being softened by the processes 

 of decay. Their comminution is due to the action of the Ostxacoda, es- 

 pecially Cypridopsis and the aquatic beetles belonging to the families Hy- 

 drophylidae and Dji"iscidae. The specific gravity of the former is slightly 

 greater than \Aater and that of the latter slightly less. A piece of floating 

 plant stem is covered with Ostracoda. A bit of the stem is often torn oft" 

 by one of these ostracods. The ostracod remains attached to it until it 



