IN THE ANIMAL KINGDOM. 19 



muscles, those of the rectum, and in the only rapidly and constantly acting muscles of 

 the gasteropods, namely those used in biting and rasping. 



To connect its occurrence in the nervous chain of Aphrodite aculeata with its prop- 

 erties is more difficult, since we have no knowledge that this annelid is remarkable for 

 nervous energy. The large bulk of the animal in proportion to the size of the nervous 

 system, and the deficient respiration, indicated by the very slightly developed vascular 

 system and the total absence of hemoglobin from the fluids of the worm, may be a reason 

 for the endowment of the nervous center which has to control such a large and compli- 

 cated organism with a special facility for appropriating what little oxygen may come 

 in its way. 



The complete absence of hemoglobin from Leptocephalus is an example of the 

 submission of an auxiliary, but not an essential, structural attribute to an all-powerful 

 necessity that of transparency. The absence of hemoglobin from the transparent 

 annelid Alciope may be similarly correlated. 



MacMunn (loc. cit.) in his studies of the distribution of hemoglobin, 

 myohematins, and histohematins in insects attributes a relationship between 

 the degree of activity of the musculature of the wings and the quantity of 

 coloring matter. Likewise, Velichi (loc. cit.) found hemoglobin in the 

 most used muscles of gasteropods, which are the pharyngeal. 



In a recent article (Archives de Zoologie experimentale, 1903, 31) on the 

 respiratory pigments in relation to the alkalescence of the blood, Gautrelet 

 states that hemocyanin replaces hemoglobin under the following conditions : 

 (a) if the diet contains Cu instead of Fe; (6) where the exchange of O 

 and CO 2 is low (hemoglobin having about 4 times the O-capacity of hemo- 

 cyanin) ; (c) if the salt capacity of the body-fluids is such that erythrocytes 

 can not exist; (d) if a large liver retains the iron. One or more of these 

 conditions may be present, but the appearance of one does not necessarily 

 imply that one or the other of these coloring matters is present. Alkales- 

 cence and the amount of coloring matter he found to be parallel. 



The distribution of hemoglobin throughout the vertebrates is univer- 

 sal, with the exception of Leptocephalus and possibly Amphioxus, and it is 

 invariably confined under normal conditions to the erythrocytes and the 

 structures in which these corpuscles are formed or destroyed. In the body 

 tissues it appears chiefly in the form of myohematins. A number of com- 

 pounds and derivatives, normal or abnormal, may be present. 



A large number of coloring matters related and unrelated to hemo- 

 globin have been found in both invertebrates and vertebrates, but a further 

 consideration is not possible within the necessarily limited compass of this 

 memoir. 



THE SOURCE OF HEMOGLOBIN PROBABLY IN CHLOROPHYL. 



The close chemical relationship of chlorophyl and hemoglobin suggests 

 either that both have sprung from a common source or that hemoglobin 

 has had its source in chlorophyl, there probably occurring in the latter case 

 a gradual synthesis during the progress of evolution. We find in certain of 

 the lowest organisms a modified form of chlorophyl or chlorophylloid pig- 

 ment; in others chlorophyl; in other forms of life occur coloring matters 

 which are identical or nearly identical with certain hemoglobin derivatives; 

 later, bodies in the form of histohematins and myohematins; and ulti- 

 mately, hemerythrin, chlorocruorin, hemoglobin, etc. 



