366 SECTIONAL TRANSACTIONS.— D. 



A series of films prepared under the direction of Dr. J. S. Huxley 

 and Mr. H. R. Hewer, shown by courtesy of the Gaumont-British 

 Instructional Co., Ltd., including, among others : 



Heredity. 



Sea-urchin, Parts I and II. 

 Animals of the rocky shore. 

 Polyps and jellyfish. 



Saturday, September 4. 



Excursion to Dovedale and the Peak district. 



Monday, September 6. 



Prof. C. M. Yonge. — The biology of certain Prosobranch Gastropoda 

 (Aporrhais and Pterocera) (lo.o). 



Unlike the Lamellibranchia, which are a homogeneous Class, the Gastro- 

 poda have become specialised for a wide variety of habitats. The most 

 striking examples are the planktonic and parasitic groups. But specialisa- 

 tion amongst the bottom living Prosobranchs is equally important. The 

 cases of Pterocera and of Aporrhais are here discussed. 



The primitive Prosobranch may be regarded as an animal possessing a 

 creeping sole, a radula used for scraping, and a digestive system capable 

 of dealing with an omnivorous diet. Such an animal would creep over 

 rocks and feed on the encrusting flora and fauna. 



Pterocera is a genus of the Strombidae common in the Indo-Pacific. 

 The animals live on the sandy areas on the surface of coral reefs. The 

 elongated operculum is dug into the sand and the animal moves by a series 

 of convulsive contractions of the pedal muscles. The radula is adapted for 

 cropping delicate algae, and the digestive system possesses not only a crystal- 

 line style — indicating a herbivore feeding on finely divided food — but also 

 a powerful cellulase for breaking down the cell walls of the algae. 



Aporrhais, undoubtedly allied to the Strombidae, lives in northern latitudes 

 and down to considerable depths on muddy bottoms. It is specialised for 

 burrowing in mud. Movement over a hard surface is essentially the same 

 as in Pterocera. Feeding is by means of an extensile proboscis armed with 

 a radula adapted for seizing particles of organic debris. The gut possesses 

 a style and there is a complicated sorting mechanism in the stomach but no 

 cellulase. 



Mr. J. Z. Young. — The structure and functioning of the higher nervous 

 centres of Cephalopods (10.30). 



The behaviour of Octopus, Squid and Cuttlefish is probably more com- 

 plex than that of any other invertebrates, but no thorough study has yet 

 been made either of their capacities or of the structure of their central 

 nervous system. The present investigation of the morphology and con- 

 nections within the nervous system has shown that besides possessing nerve 

 fibres larger than those of any other animal, making possible the very quick 

 darts of a Squid through the water, these animals also have very elaborate 

 higher nervous centres, containing immense numbers of smaller neurons. 



