ON EGGS OF MARINE ANIMALS n 



culturing diatoms to feed animals are now available. The most 

 used is Allen's modification of Miquel's for culturing Nitschia. 

 (Allen, 1907-1910; Miquel, 1890-1893; 1907.) My own method 

 (Just, 1922) however is much simpler and in my experience 

 superior. This follows: 



At the beginning of the season, mud is taken from eel grass 

 (Zostera) together with animal and plant life. This is placed 

 in jars containing sea-water equal in amount to that of the mud. 

 The jars are then covered with glass plates and set aside in 

 subdued light. In a day or so all metazoa — worms, Crustacea, 

 ascidians, etc. — are dead. After a period of putrefaction the 

 culture purifies itself and a rich growth of diatoms is apparent. 

 It is a good plan to start several such cultures at intervals of five 

 to ten days. 



From the stock cultures thus prepared diatoms are removed, 

 suspended in filtered sea-water, and strained through bolting 

 silk. The diatoms that pass through the bolting silk are placed 

 in the dishes containing the larvae. As the larvae increase in 

 size and vigor, food is added in greater quantities. 



With this method I have raised Platynereis embryos to adult 

 worms in one-half-gallon Mason jars kept tightly sealed and 

 never once opened during ten months. 



My experience in rearing marine invertebrates from eggs — • 

 Jsterias, Jrbacia, Echmarachnuis, Nereis, Platynereis, Pecten- 

 aria, Diopatra, Chaetopterus and Mytilus, etc. — indicates that 

 the most essential point is to know when to begin feeding. In 

 general, food must not be given until the larvae have used the 

 oil and yolk present in the eggs. In all forms in which the oil 

 is well defined, the time for feeding is readily ascertained. 

 Where, as in echinoderms, the oil is not so clearly marked, one 

 must make a few trials which will indicate the proper time for 

 the introduction of the food. 



Indicia for Normal Development 



Once the worker has assured himself that he has normal eggs 

 by having obtained normal development from them, he can soon 

 learn to distinguish from the eggs themselves what their develop- 

 ment will be. This knowledge will not only save time but also 

 facilitate his work. If it is possible for him to know in a few 



