340 SECTIONAL TRANSACTIONS.— D. 



Monday, September 8. 



Mr. C. B. Williams. — Migration among the Lepidoptera. 



Mr. N. N. MuRTi. — The Physiology of the Heart of larval Starfish and Sea- 

 Urchins. 



The larval heart of Echinus and Asterias makes its appearance first as a clump 

 of two or three cells on the dorsal aspect of the larva a little above the junction of the 

 oesophagus and the stomach, immediately to the right of the pore-canal. These cells 

 are budded off from the anterior coelom and later they form a vesicle. At a more 

 advanced stage, in Echinus, the ventral wall is invaginated into the vesicle and there- 

 fore bears to the vesicle the same relation as the heart of a vertebrate does to the 

 pericardium. 



Rhjrthmical contractions of this sac can be clearly seen when the larva is placed 

 with its dorsal surface up, in a drop of water, on a slide under the microscope. There 

 are as many as 35 pulsations per minute in the case of Echinus and only about 12 

 in the case of Asterias. The pulsations travel from the floor of the sac upwards 

 exactly like the peristalsis of the intestine. The effect therefore is to drive the con- 

 tained fluid upwards. This fluid, however, is the ordinary blastocoelic fluid and the 

 heart is in communication with the blastocoele. The fluid contained especially in the 

 heart of Echinus stains more deeply than that in the rest of the blastocoelic ground 

 substance, and the suggestion seems justified that this difference in the staining 

 capacity is due to the exudation of digested material, from the stomach cells. If 

 this suggestion is justified the object of the heart is to drive the nutritive material 

 forwards towards the region of the larval mouth and larval brain in Echinus, and to 

 the apical end and tissues removed further away from any other nutritive fluid, in 

 Asterias. 



The heart certainly persists in the adult life of the star fish and the sea urchin. 

 But owing to the growing opacity of the body wajl during the metamorphosis of the 

 larvae its movements cannot be seen. The structure and relationship of this organ 

 bear a close resemblance to the pericardium of Balanoglossus. 



Mr. W. E. SwiNTON. — The Plesiosaurs in the Bristol Mxiseum. 



The Bristol Museum contains a collection of Plesiosauridae second only to that of 

 the British Museum. Eight specimens of particular interest are exhibited and seven 

 of these are types. Interest also attaches to the fact that the first description of four 

 of these was made to the British Association in 1839 by Sir Richard Owen. The 

 specimens Ure : — 



Gerri&^Plesiosaurus {sensu strictu). 



PlesioSaurus conybeari, Sollas. Skeleton and skull from the Lower Lias of Blackven 

 W-ater; <;^armouth. Original description, Sollas, 1881, Q. J. G. S., xxxvii., pp. 440-81. 

 pis. 23 & 24. Lydekker cast doubt on the skull belonging to the skeleton but there 

 appears no good reason for the belief that they belong to different species or individuals. 



Plesiosaurus brachycej)halus. The type skeleton (part and counterpart) collected 

 from the Lower Lias of Bitton, Glos.,in 1830, and described by Owen in the Report of 

 the British Association for 1830, p. 69. This species was originally separated from 

 P. macrocephalus, Owen, on the characters of its cervical vertebrae. The distinctive 

 features are almost certainly due to age and the species are now grouped together 

 under the latter name. This particular specimen, never adequately described, gives 

 an excellent idea of the whole structure of the creature, including the shoulder girdle. 

 Genus Eretmosaurus. 



Eretmosauriis riigosus (Owen). The type vertebrae of Plesiosaurus rugosus described 

 by Owen (Rept. Brit. Ass. 1839, p. 82) from the Rhaetic bone bed, Aust Cliff. The 

 vertebrae were distinguished, among other characters, by the rugosity of the non- 

 articular surfaces of the centra. Actually the species is distinct, but "this character 

 of rugosity is more widespread than Owen suspected. After studying the characters 

 of the pectoral arch of a specimen of P. rugosus in the British Museum, Professor 

 Seeley created the genus Eretmosaurus with P. rugosus as the type species. The 

 validity of Seeley's genus is doubtful, as the pectoral girdle is much obscured and where 

 not obscured is unlike Seeley's figures. 



