184 SUMMAKY OF CQKRKNT RESEAKCHES RELATING TO 



a special vacuole-layer, which must be regarded as part of the dioptric 

 apparatus. 6. There is a distinct bilateral symmetry on each side of 

 a plane through the lens-groove externally and -the " raphe " internally. 

 Very important is the conclusion that the Pantopod eye develops 

 from a simple insinking of the hypodermis, and not from an invagina- 

 tion, as Morgan concluded. It belongs to the " convertiertes " not to 

 the " invertiertes " type of eye. It is relatively primitive, one-layered 

 not three-layered, and with an irregular arrangement in some of its 

 elements, e.g. the " rod-framework." So far as the eye throws any light 

 on affinities, it seems to Sokolow to point to some relationship with Arach- 

 nids, but to an independent and older origin. 



e. Crustacea. 



Red Sea Anomura.* — W. Eiddell reports on a collection of Anomura 

 made by C. Crossland from the Sudanese Red Sea. It includes seven- 

 teen species, in twelve genera. There are no new forms, but the collection 

 includes the first recorded female of Cestopagurus coutieri Bouv., and 

 the author adds something to Nobili's description of GaJathea humilis Nob. 



Pigment-migration in Eye of Crayfish, f^ — Edward C. Day has 

 experimented with Camharus affinis on the effect of coloured light on 

 pigment-migration in the eye. Different regions of the spectrum at 

 equal intensity elicited different amounts of pigment migration. Blue- 

 violet was more potent than red, as evidenced both by sections and by 

 direct observations of the eye. Blue-violet, green and yellow, ranked 

 close together, but of the three blue-violet was probably the more efficient 

 in evoking the migration. The rate of migration varied with the phy- 

 siological constitution, being slow in a feeble or sluggish animal and 

 more rapid in a vigorous one. A bleaching of colour from metallic 

 orange to red, and then to dull yellow, was observed in the eye exposed 

 to light. The possibility is that this phenomenon is due to a chromatic 

 substance located in the rhabdomes, which undergoes a partial bleaching, 

 and is analogous to visual purple in the vertebrate retina. 



As to the use of the pigment, the theory now most generally accepted 

 is that the pigment serves to regulate the amount of light entering the 

 receptive organ, and to give better definition to the image by preventing 

 irradiation. As to what actually brings about the migration, there is 

 evidence that the migration of the pigment is induced primarily by the 

 direct stimulus of light, while it may be that the central nervous system 

 exerts a secondary influence upon it, perhaps of sUght inhibition or of 

 occasional stimulation. In the direct response of the pigment, there 

 may be an intra-cellular actuating force, or an extra-cellular or chemo- 

 tropic force, and the author discusses the evidence. It is tentatively 

 suggested as a final explanation of the pigment as a protective mechanism, 

 that it is correlated with the sensitivity of the receptive organ to those 

 wave-lengths which stimulate them to the greatest chemical activity. 



* Journ. Linn. Soc. (Zool.) xxxi. (1911) pp. 260-4. 



t Bull. Mus. Comp. Zool. Harvard, liii. (1911) pp. 305-43 (5 pis.). 



