52 CULTURING OF AMPHIBIAN EMBRYOS 



A. Anura : 



After metamorphosis the situation becomes reversed in that the Anura require living, 

 moving food. Living earthworms cut into 1 -inch pieces, which will continue to move 

 and attract the small frogs, are excellent as food. Blow flies, meal worms, ants, 

 spiders, roaches, caterpillars, grasshoppers, will all be eaten as long as they move. 

 Fish muscle, mammalian liver or muscle, dipped in a thin paste of Brewer's yeast 

 and cod liver oil is an excellent food for recently metamorphosed frogs. 



Xenopus is a slight exception in that it will eat anything bloody, particularly strips of 

 raw liver. This form shows little activity except in taking of food, after which it 

 settles down in the water again for as long as several days, coming to the surface 

 only occasionally to get air. 



Some of the potentially larger Anura (e. g. , R. catesbiana, the bullfrog) may grow 

 rapidly and will require more food. These forms may be fed small crayfish, min- 

 nows, earthworms, and even small frogs of the same or other species. It is pos- 

 sible but difficult to train Anura to take non-living food. 



The tree frogs (Hyla) require a continually humid environment such as an ordinary 

 terrarium and their food consists of small insects. If the terrarium is glass covered, 

 Drosophila (vestigial mutant) may be given to them, but it takes a good many flies to 

 iTiake an adequate meal. Hyla will take other living food such as earthworms. 



Toads require a rather warm and dry environment, live on insects at first and then 

 they will accept worms and even strips of beef, if the food is shaken before thier nos- 

 trils. 



B. Urodela : 



Salamanders are aquatic or semi-aquatic, and a few are actually terrestrial, hence 

 the food requirements will vary somewhat with the species. 



In general, the salamanders should be removed to a large crystallizing dish during 

 feeding. The food at first may consist of clumps of white worms (Enchytrea), small 

 earthworms or larger earthworms cut into 1 -inch lengths suitable for ingestion. As 

 the salamanders grow they can be trained to accept strips of beef or calves liver, if 

 the liver is held in forceps and dangled before their nostrils. These forms act as 

 though they are blind, but their olfactory senses are acute. After the feeding, re- 

 move all excess food, rinse off the specimens in fresh water, and return them to 

 their tanks. Uningested or regurgitated food in the tank necessitates frequent com- 

 plete change of medium, and occasional sterilization of the entire tank. 



Triturus pyr rhogaster, the Japanese fire salamander, should be fed about three times 

 each week, and each adult specimen should receive the equivalent of about 1 inch of 

 liver, the diameter of a small pencil. With this routine they may be kept in healthy 

 condition for many years, producing eggs (under pituitary stimulation) when desired 

 by the Investigator. 



SPACE AND OXYGEN 



The space factor in development has not been adequately recognized but it plays a very 

 important role in the rate of development. In general, the larvae will grow the faster in 

 less crowded conditions, all other factors being equal. It is suggested that a ratio of 1 

 egg to 2 cc. of medium be used in finger bowls with a maximum of 25 eggs to 50 cc. of 

 medium. As the embryos develop into larvae (tadpoles) this ratio will have to be changed 

 so that at the beginning of feeding there are no more than 10 tadpoles per finger bowl of 

 50 cc. of medium. At this time it is better to transfer the tadpoles to a larger tank to 

 allow for greater activity (see Rugh, 1934). 



