54 



aniR-.als v-ith different thermal optima that have no blood, but take 

 in oxygen directly throu^rh their epithelial surface, all of the 

 coelenterates , for example? 



Very little, too, is kno'vn aoout the respiration of the marine 

 majnmals; sundry interesting problems spring to mind in this con- 

 nection. How must we assay as factors governing the distrioution, 

 the seasonal activities, and a host of other phenomena that are 

 controlled to a greater or less degree by temperature, the existence 

 of well defined critical temperatur-s such as have D^en made out, 

 both in a Natural History way, and experimentally? 



Te even know very little about the actual internal temperature 

 of marine animals compered to thtt of the watrr in which they live. 



The tempe^rature problem is not only one of the most important in 

 vital econom.y, but has the added advantage (from the practical 

 standpoint) that temperature is a convenient factor with which to 

 work, being readily controlltd under experimental conditions, while 

 the effects are readily measured. 



Other comp.rative studies of this sort, which can favoraoly be 

 carried out on s--a animals, mia-ht prove of assistance to the human 

 physiologist in his attempts to interpret the phenomena he has to 

 deal with. Especially interesting in this connection is the occur- 

 rence in maiTamalian blood of salts in proportion similar to sea water, 

 with the contrastins: fact that while, in sea fishes, the body fluids 

 are nearly the same as s-a wat-r in this respect, they are never 

 precisely so. The whole Question of the physiological significance 

 of the different salts is, in fact, a most important one, to explain 

 which no satisfactory theoretic basis has yet been arrived at. For 

 studies in this field sea water is again the most favorable environ- 

 ment. Here new lines of attack are opened by recent advances in the 

 physical-chemistry of salt solutions, for Fhich marine animals, 

 because of their simplicity, are the most promising subjects. 



In like manner, the key to the riddle of the secretion of gas, 

 over which there has been much controversy in the field of pulmonary 

 respiration, m.ay well be found in the physiology of the swim bladder 

 of fishes, about which little is yet known with certainty. Many 

 Questions of nutrition, too, such as might well be attack:;d in 

 marine animals, would find their reflection in the physioloay of the 

 higher animals - so, too, the manner of excretion of waste products 

 by the anim^al groups that have no special organs for that purpose. 

 This, for example, would include the intra-cellular pigments, and the 

 crystalline secretions of medusae. 



Calcium; metabolism, as reflected by the deposition of limis salts 

 in bones, is another field on which studies in marine physiology 

 should throw much lisrht. Thus the rele^tion betw-en oc'^^an tem.p^rature. 

 the occurrence of lime-secreting animals, and the amount of lime they 

 secrete, sua-grsts th i importance of investigations into the role 

 played in calcium secretion by the effect that other electrolytes may 

 have on the solubility of calcium carbonate. 



In the whole field of the physiology of licrht, too, especially 

 attractive subjects are to be found among the great variety of marine 

 animals of widely divergent groups thot liv- normally in regions of 



