268 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



Thus, in regard to sponges, lie states that the bright colours (" warning 

 colours ") of certain forms are not associated with the inedibility, and 

 that there is great colour variation. Again, the common cross-fish, to- 

 gether with other common Echinoderms, is brightly coloured, is con- 

 spicuous in natural conditions, but is attacked by birds, fish, and by the 

 related sun -star. The difficulties in regard to the coloration of the 

 Nudibranchs are also discussed in some detail. 



New Theory of Coloration.* — Georges Bohn suggests a new point 

 of view in regard to coloration. Caruot has shown that pigment 

 granules are not mere precipitates in the cell-plasma ; they are mobile 

 cliromogenic elements. They can migrate within the organism and even 

 pass from one organism to another. Here the author refers to Miss 

 Newbigin's Colour in Nature, and to a book of his own. The Crus- 

 taceans parasitic on Ascidiella and Botrylloides are invaded by the pig- 

 ment granules of their host. There seems to be a struggle between 

 chromogeuic granules unequally or diversely coloured, for the corpuscles 

 have some measure of vitality. The homochromic colouring of plants 

 and animals living in close association, and the changes of pigmentation 

 in the course of development, are among the facts which Bohn seeks 

 to interpret by his hypothesis. He seems to regard the pigment as 

 originally the result of a nuclear excretion or emission, and the pig- 

 mentation as in part the result of a struggle among the granules. 



Tunicata. 



Heart of Salpa.t — Dr. L. S. Schultze has made an extended series of 

 observations and experiments on the action of the heart in Salpa, and 

 the causation of the periodic reversal of the circulation. Observations 

 on intact specimens showed not only the existence of individual and 

 specific variation in the number of similar beats, and so on, but also the 

 sensitiveness to alterations of environmental conditions, especially as 

 regards the amount of oxygen in the water. Further, a series of experi- 

 ments showed that (1) the isolated heart beats normally ; (2) the con- 

 tractions are not dependent on the presence of blood in the heart ; (3) 

 the nerve-ganglion is incapable of affecting the pulsations ; (4) the heart 

 itself contains no nerve-cells or fibrils capable of influencing the con- 

 tractions. The author's conclusion is, therefore, that the spontaneous 

 contractions of the heart are entirely myogenic in origin, depending 

 upon stimuli which originate in the course of the metabolism of the 

 muscle-cells, which are exceedingly rich in sarcoplasm. All parts of 

 the heart are capable of originating a series of rhythmic contractions, but 

 under normal conditions it is the two ends only which constitute the 

 centres of origin of the stimuli. If these centres be called A and B, it 

 is obvious that there are three elements in the phenomenon of reversal : 

 (1) the inhibition of the peristaltic wave (originating from A); (2) tho 

 pause; (3) the commencement of the antiperistaltic wave (originating 

 from B). Briefly put, the problem is then the means by which centre A 

 periodically gains the mastery over centre B, or vice versa. The author's 



* Compter Rendu:;, cxxxii. (1901) pp. 173-5. 



t Jenaische Zeitsclir. Naturwiss., xxxv. (1901) pp. 221-328 (3 pis. and 5 figs.). 





