ZOOLOGY A.ND BOTANY, MICROSCOPY, ETC. 457 



White barnacle-covered rocks have more white whelks than have mussel- 

 beds a few feet away. Those living on rocks near mud-flats are darker 

 than those on the more exposed parts of the same islands. Where the 

 struggle for existence is greatest on the exposed islands and the muddy 

 harbours, selection tends to preserve the dark-coloured and the lamellated. 



Nervous System of Crepidula and its Development.* — Harold 

 Heath has examined the nervous system in Crepidula adnnca and C. nivea, 

 and studied its development in the former species. The central nervous 

 system in C. aduma is situated in the base of the neck, in a spongy mass 

 of connective tissue, placed between the pedal musculature and the over- 

 lying mantle cavity. It conforms to the highly-centralized type cha- 

 racteristic of the Monotocardia generally, with cerebral, pleural, and 

 pedal ganglia closely appressed. A description is given of the buccals 

 (slightly attached to the dorsal surface of the radula musculature), 

 the elements of the visceral loop (sub-intestinal, supra-intestinal, and 

 visceral), and the osphradial ganglion situated far forward on the left side 

 of the mantle cavity. 



Shortly after the first appearance of the foot, the ectodermic cells 

 immediately in front of the lateral angles of the mouth-opening commence 

 to elongate, and each area forms a well-defined, probably sensory, ridge 

 and the tentacle. A migration therefrom forms the cerebral ganglia. 

 Synchronous with this, cells migrate inwards from the foot and form 

 the pedal ganglia. Sections give no indication of cell-division after the 

 cells have left the ectodermic layer. The same is true of the other ganglia. 



The buccal ganglia are the only ganglia which do not directly arise 

 from cells migrating from the overlying ectoderm. They seem to be 

 products of the cerebral ganglia. The origin of pleurals and viscerals is 

 described. 



Scottish Nudibranchs.f — W. Evans and W. E. Evans contribute some 

 notes on Nudibranchs from the Firth of Forth. An addition to the local 

 list is the minute Hermaea dendritica, which feeds on Bryopsis and 

 seems to pass through two generations in the year. Another minute 

 form (9-10 mm.) is LamdUdoris aspera, which might be readily passed 

 over as a young stage of one of the larger Dorids. Interesting also is the 

 minute Planarian-like Limapontia nigra. 



Artbropoda. 

 a. Insecta. 



Relation between Gonads and Secondary Sex Characters in 

 Insects. J — E. A. Cockayne discusses the possibility of there being in 

 insects a relation between the gonads and secondary sex characters, such 

 as is found in Vertebrates. Experiments in castration and transplanta- 



• Proc. Acad. Nat. Sci. Philadelphia, Ixviii. (1917) pp. 479-85 (2 figs.). 



t Scottish Nat., No. 65 (1917) pp. 105-10. 



X Trans. Entomol. See. London, 1916, parts iii.-iv. (publ. 1917) pp. 336-42. 



