1920] Richmond, Studies on the Biology of the Aquatic Hydrophilidce 9 



Dytiscidae but swim about on the surface until they regain shore or 

 find some plant to aid them in descending. An examination of the 

 banks adjacent to the collecting grounds at the time of transformation 

 will offer good collecting because often the larval skin, pupal skin, and 

 adult may be procured in the pupal cell at one time. Some of the 

 species are attracted by arc lights during warm nights and, in fact, it is 

 there that Hydrous is most frequently obtained. 



Methods of Rearing 



The isolation, according to species, of adults, which readily lay eggs 

 in captivity, proved the best method of acquainting oneself with the 

 immature stages. Newly hatched larvae are thus easily obtained. The 

 most advisable temporary aquarium for such work seems to be a small 

 stender dish. A small stone, half submerged in the water and draped 

 with Cladophora gave excellent conditions for egg laying, especially for 

 the smaller beetles which, as a rule, lay their eggs in moist places and 

 not directly in the water. 



For larva?, larger containers produce better results. Moreover, 

 they should be arranged as aquaria-terraria, for many of the adults and 

 larvae spend most of their time on shore. In preparing this, it is best to 

 get some mud from the bottom or edge of a pool and, after placing it in 

 the container to the depth of about an inch, slope it up gradually so 

 that it forms a miniature bank. The bank end should be normally high 

 enough so as to be a little dry on the surface. Cladophora and money- 

 wort make the best plant materials because of their cleanness and last- 

 ing qualities. As a rule, the container should be filled so that the bank is 

 covered and then placed in the sun. In a few days, the time depending 

 on the conditions in the pool where the mud was obtained, numerous 

 entomostracans destined to be food for the future larvae will be present. 

 The vegetation is then added. 



The larvae, when fully grown, seem restless and try to crawl out. 

 If the time for transforming has arrived, they rapidly burrow down and 

 form their pupal cells. Some, however, pupate on the surface of the 

 terrarium, evidently not liking the conditions below. Slightly moist 

 earth seems to be the most natural substance for the terrarium and an 

 inch or so depth will suffice. If not too deep, they will often make their 

 cell next to the glass container, where it is favorable for observation. 



