10 BASIC METHODS FOR EXPERIMENTS 



from Memhranipora pilosa that had been shipped to her; these 

 eggs she claimed were normal. I was never able to obtain 

 viable eggs of this species at Naples except from freshly collected 

 animals. The larger marine teleosts with few exceptions deteri- 

 orate rapidly after capture during the breeding seasons. In the 

 case of the gametes themselves viability may diminish even more 

 rapidly. A moribund egg is fit only for work which aims to 

 study death changes and is valueless for experiments since it is 

 incapable of giving us the necessary normal control. When 

 therefore eggs and sperm are transported, they may be used only 

 on the basis of sure knowledge that they have not suffered. 

 The rule of paramount importance for the experimental embry- 

 ologist is to use animals freshly collected and only from these, 

 eggs and sperm freshly deposited or removed. 



On the basis of his knowledge of development in the field, the 

 experimenter can soon learn to know whether or not the develop- 

 ment in the laboratory is normal. This knowledge, I repeat, is 

 the sine qua non of all experimental work in embryology. For 

 not only is normal development the main object of study, but it 

 also represents the control of experiment and thus determines 

 the quality of interpretation. Therefore, the investigator 

 should, however laborious and long-ienduring the task, follow 

 the development of the egg in the laboratory and know that this 

 is normal, before he begins to set up an experiment. 



In the laboratory I have carried eggs oi Platynereis megalops 

 through to sexual maturity and from the eggs and sperm 

 obtained reared a second and from the second a third generation 

 of worms. At Naples I have reared P. dumerilii to sexual 

 maturity ; at Woods Hole, Nereis limhata. Ciona I have reared to 

 sexual maturity (Naples). At Roscoff I have reared Perinereis 

 cultrifera from eggs fertilized in the laboratory which reached a 

 length of 4 cm., when I had to abandon the culture. In addi- 

 tion, I have reared to adult condition several species of sponges 

 (Naples), hydroids (Naples), Echinarachnius (Woods Hole), 

 Asterias forhesii (Woods Hole), Diopatra (Woods Hole). 



Method for Diatom-Culture 



Perhaps the greatest difficulty in rearing animals from eggs 

 fertilized in the laboratory is feeding them. Several methods for 



