188 SUMMARY OF CURRENT RESEARCHES RELATING TO 



INVERTEBRATA. 



Slollusca. 

 y. Gastropoda. 



Centrifuged Eggs of Crepidula.* — E. G. Conklin subjected the eggs 

 of this marine Gastropod to centrifugal force approximately two thousand 

 times gravity. The yolk is thrown to the distal or centrifugal pole, the 

 oil and other light substances to the centripetal pole, while the nucleus 

 and centrosphere, together with most of the cytoplasm, occupy the 

 middle zone between the other two. If there is time in fertilized eggs 

 before the first cleavage, there is a restoration of the normal positions. 

 If cleavage occur before restoration, the two daughter-cells have an 

 abnormal distribution of substances. But in them there is speedy 

 restoration to something like the normal. By organic regulation there is 

 a restoration of the normal polarity and pattern. There seems to be a 

 " ground substance " which is not moved by the centrif uging — a frame- 

 work of protoplasmic strands which preserve the relative positions 

 of nucleus and centrosphere in the cell-axis. 



British Terrestrial and Fresh-water Mollusca.f — John W. Taylor 

 deals, in Part 23 of his Monograph, with Hygromia, Ashfordia, and Theha, 

 and announces, we regret to see, that the work must be suspended until 

 the conclusion of the War. 



Immunity Coloration in Nudibranchs.$ — W. J. Crozier refers 

 particularly to the large brilliant Chromodoris zebra of Bermudas. Its 

 pattern is an irregular streaking of yellow or orange upon a field of blue. 

 Large numbers are found in quite shallow water, though they go down 

 to 10 fathoms. The skin secretions are repugnant to many animals, and 

 the odour is penetrating and disagreeable. The repelling material 

 contains globules of the blue pigment, but the main constituent is a 

 coagulated white substance containing only globules. Cloth bags con- 

 taining the nudibranch are avoided by fishes, and blinded fishes are also 

 repelled. The success of Chromodoris in the shoal waters of the coral- 

 reef region is conditioned by the secretion ^nd the odour, and by the 

 unpalatable nature of the jelly surrounding the eggs. The eggs develop 

 slowly, but the animals reproduce throughout the year. Crozier accepts 

 Reighard's reasonable theory that the startling colours have arisen for 

 internal physiological reasons under conditions of immunity which have 

 been attained by characters other than those of coloration. " The 

 coloration of C. zebra is a metabolic accident, at least in regard to its 

 protection, for a single experience with a normally coloured specimen is 

 sufficient to cause snappers, turbots, and groupers to have nothing 

 to do with subsequent individuals offered to them, even though these 



* Proc. Nat. Acad. Sci. U.S.A., ii. (1916) pp. 87-90. 



t Monograph of the Land and Fresh-water Mollusca of the British Isles, 

 Part 23, pp. 65-112 (4 pis. and many figs.). 



X Proc. Nat. Acad. Sci. U.S.A., ii. (1916) pp. 672-5. 



