§1] 



UPON THE RATE OF GROWTH 



365 



of 3.8%. Anything which favors endosmosis seems, within 

 certain limits, to favor growth. 



Regenerating annelids liave also been studied at my labora- 

 tory by Mr. J. L. Fkazeue. A large number of worms of a 

 species of Nais, all of approximately the same size, were cut into 

 two parts. Of these the anterior, consisting of twelve seg- 

 ments, was alone preserved for experimentation, and was placed 

 in water either pure or containing a variable amount of com- 

 mon salt in solution. At the end of ten days the anterior 

 piece had regenerated at its tail end a certain number of seg- 

 ments varying with the strength of the solution as shown in 

 the following : — 



TABLE XXXIX 



Showing the Average Number of Segjiexts of Nais regenerated per Day 

 IN Various Solutions or Sodium Chloride 



The decrease in the number of regenerated segments was 

 thus, with increasing concentration, at first rapid, then slow. 



Fission, which is so closely bound up with growth that we 

 may treat it as an index of growtli, is also controlled by the 

 concentration of the medium. Mr. P. E. Saegext has, at my 

 suggestion, studied this subject in the naid Dero vaga. This 

 species divides so rapidly that ordinarily it doubles its numbers 

 every ten days. The worms were kept in solutions of varying 

 concentration of various salts. They were reared in similar 

 jars, supplied with similar food,* and kept under otherwise 

 similar conditions. A definite number of worms having been 

 put in each jar, the increment at the end of ten days was deter- 



* 1 to 2 CO. of corn meal extract was added every day to the 200 cc. of water 

 in which the worms were living. 



