490 PATON— CORRELATION OF STRUCTURE [Apn' '8. 



living embryos when placed in various solutions respond with great 

 rapidity to even relatively slight temperature changes occurring in 

 the surrounding media. In the case of the pulsation of the heart 

 many investigators, among whom are Snyder, Carlson, v. Tschermak, 

 and others, determined the temperature coefficient in connection with 

 the activity of this organ. As far as I have been able to determine 

 the extreme sensitiveness of the heart as regards rises in tempera- 

 ture seems to be somewhat greater, or at least the responses are 

 quicker, at a period when the development of the nervous system 

 is well advanced than at earlier stages in the life of the embryo ; and 

 I believe the same law holds true with regard to other reactions of 

 the organism. These facts afford an interesting confirmation of the 

 results of observations made by A. G. Mayer with a view to deter- 

 mining the relative importance of the nervous system in the medusa. 

 Mayer has shown that there is greater sensitivity for heat when the 

 muscles remain in contact with the sense-organs than when the con- 

 nections are severed. The general character of the responses of the 

 embryo in regard to heat, prior to or subsequent to the development 

 of the nervous system, are in a measure comparable to the variations 

 of adjustment of jellyfish for similar stimuli when muscles are either 

 deprived of connection with or allowed to remain in contact with 

 sense organs. In the vertebrate embryo as well as in the medusa the 

 extreme delicacy of response is dependent upon the presence of 

 nerve-elements, and when these have not developed or have been 

 eliminated by experiment the capacity of adaptation of the organism 

 is correspondingly lowered. 



The technique used in the experiments is the same in all cases. 

 The chief precaution necessary is to avoid as far as possible sub- 

 jecting the embryos to changes in temperature and all rough hand- 

 ling; so that the results may not be complicated by the introduction 

 of too many different stimuli. 



When the eggs are taken out of the incubator they are opened as 

 quickly as possible, just inside the door of the warm box which 

 covers the microscope, and the embryos are detached from the egg 

 and lifted by means of a horn spoon into the dish containing the 

 solution (NaCl 0.9 — CaCla 0.02 — KCl 0.02 — NaHCoa 0.02 — 



