574 SUMMAP.Y OF CURRENT RESEARCHES RELATING TO 



The pineal substance responsible for the pigment changes is wholly 

 extracted by acetone. The residue after acetone extraction is an inert 

 substance as far as influencing pigment is concerned. But this residue 

 influences growth and differentiation. The inference is that the gland 

 contains more than one active substance. 



The reactions produced by pineal extracts add some evidence to 

 Spaeth's contention that the melanophores are modified smooth muscle- 

 cells. The similarity of contraction of certain smooth muscle organs 

 under the influence of pineal extracts, and the contraction of melano- 

 phores is in keeping with Spaeth's hypothesis. The very nature of the 

 pineal-pigment cycle affords an excellent method of approach to the 

 study of melanophore function and to the larger problems of the 

 colloidal state. 



Reactions of Tadpoles to Light. *^- William H. Cole and Carleton 

 F. Dean have studied the photokinetic reactions of tadpoles, probably of 

 Rana damitans. They showed themselves sensitive to light when a 

 length of 40 mm. or more is reached. The skin is the important 

 receptor for photic stimulation, the tail region being the most sensitive. 

 The reaction varies with the age or stage of development ; the youngest 

 stages being indifferent, the mid-larval stages being photokinetic, and 

 the final stages being positively phototropic. Previous exposure to 

 illumination or darkness has very little influence on the intensity of the 

 reaction. It is probable that the reaction is controlled by a nervotis 

 nexus, and not by direct stimulation of the melanophores. 



Colour-chaug'es of Reef-Fishes.j — W. H. Longley has spent 

 several years studying the colours and colour-changes of the West 

 Indian reef fishes with a view to throwing fresh light on the general 

 problem of the biological significance of animal coloration. The reef 

 fishes are peculiarly suited for such a study. They are richly coloured ; 

 many species may be observed in a single circumscribed area ; they 

 possess as a class a great power of colour-change ; they can be studied 

 in their natural environment ; and it is usually possible to determine 

 the nature of their food by analyzing the contents of the stomach. 

 Countershading — the definite gradation of pigment from darkest on the 

 mid-dorsal to lightest on the mid-ventral line — appears almost univers- 

 ally on reef fishes, and its absence or relative deficiency seems to be 

 definitely correlated with some unusual habit or peculiar form. Colour- 

 changes, which occur even among the most gaudy, tend to assimilate 

 them to their environment, and in general their colours repeat- those of 

 their surroundings. Specially-defended types are not unlike others in 

 pigmentation, or inferior to them in their ability to effect adaptive 

 colour adjustments. Finally, there is no evidence that brightly-coloured 

 species enjoy greater immunity from attack than others, for they 

 constitute a large proportion of the food, and may be readily identified 

 in the stomach contents of predaceous forms. These statements, which 

 rest on a great body of verifiable observations, are consistent with the 



* Journ. Exper. Zool., xxiii. (1917) pp. 361-70. 



t Journ. Exper. Zool., xxiii. (1917) pp. 533-601 (1 pi.). 



