220 Phylum A rthropoda 



Daphnias. In general, the Daphnia culture should be kept supplied 

 with fresh food, either lettuce leaves or raw flesh (preferably both) up 

 to the limit possible without making the water cloudy. This limit must 

 be learned by experience and depends upon the size of the container. 

 Whenever it is seen that the Daphnias are not flourishing as rapidly as 

 before, new food should be added. 



Daphnias may not be grown indefinitely in the same culture water. 

 From time to time it is necessary to strain out the Daphnias and place 

 them in freshly made cultures. When it is evident that the Daphnias are 

 no longer multiplying well despite addition of fresh food, they should 

 be transferred to an entirely new culture. 



References 



For the culture of Scapholeberis see below. 

 For the culture of Simocephalus see p. 207. 

 For the culture of Moina see p. 207. 

 For the culture of Moina affinis see p. 213. 



Family 



CHYDORIDAE 



CHYDORIDAE 



Charles H. Blake, Massachusetts Institute of Technology 



IN RAISING Pleuroxus hamulatus I found that a few cc. of water in a 

 Syracuse watch glass sufficed for an individual. The young were re- 

 moved to separate glasses a few hours after birth, each being provided 

 with freshwater which had been stored in contact with air and with 

 Elodea. An aquarium provided a mixed culture of Stichococcus and 

 Ankistrodesmus. [For culture see p. 227.] Enough of this was placed 

 in the watch glass to form a thin, green coating on the bottom. After 

 a few days most of it had been passed through the animal's gut and had 

 become agglomerated and no longer suitable for food. The specimen 

 was then transferred to a fresh glass made up as before. Crowding 

 caused the production of two of the hitherto unknown males but all speci- 

 mens were short-lived when crowded. Ephippia are formed in the absence 

 of males or by crowding and, as in Scapholeberis, an individual may re- 

 vert to the production of parthenogenetic eggs. Unfertilized ephippial 

 eggs degenerate. Mass-cultures were not attempted with this species, 

 but from observations in nature and on Alona guttata in the aquarium, it 

 is apparent that a relatively great volume of water must be allowed per 

 individual and an abundance of unicellular green algae as a source of 

 food. The actual food material is unknown to me since Ankistrodesmus 

 is apparently unharmed by its passage through the gut. Abundant 

 oxygen is necessary. 



