552 Phylum Echinodermata 



before the first three have been completed, these should be carried out 

 after fertilization. If the eggs are very numerous separate them into two 

 groups in 3-liter bowls. Allow only one layer of well spaced eggs on 

 the bottom of the dish. 



REARING THE LARVAE 



Free swimming blastulae rise to the surface in about 20 hours. Decant 

 these from each finger bowl into a suitable container of about 20 liters' 

 capacity nearly filled with seawater. Be careful not to carry over un- 

 fertilized eggs or dead embryos. On the following day it is advisable to 

 siphon half the contents of each jar into an empty one and to fill all 

 four with seawater. 



The meniscus in each jar must be carefully marked and the daily loss 

 of water through evaporation corrected by the addition of distilled 

 water. Stir the water gently and add the distilled water very slowly 

 to prevent large local dilutions. In this manner a relatively stationary 

 salinity may be maintained. This obviates the necessity for a circula- 

 tion of fresh seawater through the jars. Animals have been reared in this 

 manner without any further change of water. It is important not to 

 have too large a number of larvae in a culture. 



Aerate the cultures slowly. A glass tube with the lower end drawn 

 out to a fine opening (0.1 mm.) is allowed to rest obliquely against the 

 bottom of the culture jar. Clean compressed air is supplied to the glass 

 tube so that a fine stream of very small bubbles rises through the culture 

 medium. Rapid aeration produces swift currents which cause disintegra- 

 tion of larvae. Under no circumstances should rubber tubing touch the 

 seawater. The aeration is of course more efficient if air is used to set 

 up the circulation. 



The larvae require food when the stomodaeum breaks through (second 

 or third day). Mixed cultures of phytoplankton containing Chlorella, 

 Nitzschia, Dunaliella [see p. 31], and phytomonads are satisfactory. 

 The well being of the larvae is to a large measure due to the variety of 

 food. Gemmill used Nitzschia alone at first but discovered that 

 "Nitzschia plus a chance bacterial and flagellate infection provided even 

 better results." Dr. P. S. Galtsoff has used a pure culture of Nitzschia 

 [see p. 36] in raising A. j or best larvae. They became large brachiolaria 

 but never metamorphosed. 



Adjust the salinity of the food culture to that of the seawater in the 

 jars and add 5 cc. of this to each jar, three times a day. Withdraw a 

 corresponding amount of liquid from the vessels once a day to retain the 

 mark used in correcting the salinity. 



Although the critical temperature for spawning of A. jorbesi in Long 

 Island Sound is 2o°±o.5° C., the larvae can develop at a lower range. 



