48 BASIC METHODS FOR EXPERIMENTS 



Delage, Herbst and Loeb. Of these that by Delage Is best 

 (1910). It is my purpose to detail only those methods that I 

 know first hand. Also, I make a distinction that the authors 

 named above did not make, namely, that between methods for 

 inducing initial changes in the eggs without cleavage and sub- 

 sequent development and those which give development to a 

 swimming form. I think it is well to restrict the meaning of the 

 term, experimental parthenogenesis, so that it does not include 

 those effects upon eggs which do not lead to development. The 

 work on experimental parthenogenesis has suffered greatly 

 because of failure to niake this distinction. 



The best means for calling forth development of marine eggs 

 to a swimming stage is hypertonic sea-water. Its effect varies 

 depending upon the species of egg, and, for a named species, 

 upon the degree of hypertonicity. With respect to the former, 

 it may induce wholly abnormal swimming forms, as for exam- 

 ple, on eggs of worms which develop without cleavage; as to the 

 latter, it may on the eggs of echinids produce swimming forms 

 without having initiated complete ectoplasmic change. Another 

 effective means is increase in temperature. A third, acid in 

 sea-water. Hypotonic sea-water succeeds In some cases, but in 

 my judgment is a rather poor means. The same may be said 

 of radiations and some other means, whose effects have been 

 investigated. Another method consists in combining two 

 means, as the butyric acid hypertonic sea-water method which 

 really is a combination of three means, since it is only successful 

 when the eggs are placed In sea-water between exposure to each 

 agent. 



Hypertonic sea-water 



Hypertonic sea-water brings about development to the 

 swimming stage without cleavage, so-called differentiation with- 

 out cleavage, in eggs of many worms especially. Unless the 

 worker desires to make experiments on this type of development, 

 he should not use hypertonic sea-water on these eggs, as for 

 example, those of Nereis, Chaetopterus, Amphitrite, etc. If, 

 however, he has In mind to investigate differentiation without 

 cleavage, he should consult the literature on this subject for the 

 methods used. 



