THE LIVING SUBSTANCE. 3 



The new facts are not thought to explain the phenomena, 

 but only to unify them, so that the future master who shall find 

 for us an explanation may have a less incoherent mass of con- 

 tradictory evidences to deal with. 



Though it is felt that acknowledgment to those who have 

 from time to time befriended the work by giving opportunities 

 to the worker, were better left for a later and more complete 

 presentment, which should more fully justify their faith and 

 requite their kindness ; it is impossible to omit here recogni- 

 tion of help without which the work might never have been 

 done. 



To Dr. Edmund B. Wilson, who in 1888 admitted me as a 

 hearer to his class at Bryn Mawr College, I owe such technical 

 training as I possess ; and also then, and later at Wood's Holl, 

 stimulus and inspiration to research work, such as springs natu- 

 rally from contact with so gifted and catholic a mind, and such 

 as grows under an unflagging interest and practical help given 

 all who show interest in their work. 



Through the kindness of Dr. C. O. Whitman, I occupied for 

 three summers a room in the Investigator's Department of the 

 Marine Biological Laboratory at Wood's Holl, Mass., and 

 received much encouragement and stimulus, both from him 

 personally and from the environment his scientific achieve- 

 ments and genial influence create, — a circle of disinterested 

 workers who gather about him there, making an atmosphere 

 electric with enthusiasm, and holding neither method nor result 

 a secret from one another.^ 



Finally, the liberal practical aid of Dr. Horace Jayne, Dean 

 of the University of Pennsylvania, providing a private labo- 

 ratory in the Biological Department, greatly furthered the 

 work and enabled me to bring it, so far as it goes, to a satis- 

 factory conclusion during the winter of 1894. The perfect 

 optical conditions enjoyed there, the open north light and free- 

 dom from vibrations, gained me some valuable points; and 



1 I desire distinctly to free from all responsibility for my choice of a subject, 

 or its treatment, the above savants. The privileges and help acknowledged here 

 were given to aid research on the embryology of rotifers, the results from which, 

 because incomplete, are still unpublished. The present work was carried on at 

 the same time and was known to myself only, being then but fragmentary results. 



