472 Professor T. J. Parker. [June 10, 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following Papers were read : — 



I. " On the Blood-vessels of Mustelus antarcticxis : a Contribution 

 to the Morphology of the Vascular System in the Verte- 

 brata." By T. Jeffery Parker, B.Sc, C.M.Z.S., Professor 

 of Biology in the University of Otago, N.Z. Communicated 

 by Professor M. Foster, Sec. U.S. Received June 4, 1886. 



(Abstract.) 



The paper describes in detail the arteries and veins of Mustelus 

 antarcticus, comparing them with those of other elasmobranchs, and 

 with the embryonic trunks of the vertebrata generally. 



As far as the author's resources would allow, the synonymy of the 

 principal vessels is given. 



The paper is illustrated by four quarto plates, and two diagrams in 

 the text; the figures are, as a rule, made by combining the results of 

 several dissections ; the topographical relations of the chief vessels 

 are shown in drawings of transverse sections of a frozen specimen. 



The account of the vessels in Mustelus is supplemented by reference 

 to the chief vascular trunks in the embryo of Scymuus of " Stage " 

 (Balfour) ; several sections of this embryo are figured. 



The blood is taken from the heart to the gills by five pairs of 

 afferent branchial arteries, one for the hyoidean demibranch or half- 

 gill, and one for each of the holobranchs or complete gills borne by 

 the first four branchial arches. 



The blood is returned from the gills by nine pairs of efferent 

 branchial arteries, one for each demibranch ; the two efferent arteries 

 of each holobranch are united by two transverse commissures at about 

 the middle of their length, and the arteries of the adjacent demibranchs 

 of successive gills anastomose dorsally and ventrally, forming loops 

 which encircle the internal gill- clefts. 



The anterior efferent artery of each holobranch is the main re-vehent 

 trunk of the branchiomere, and is directly continued into an epi- 

 branchial artery lying dorsal to the gill ; the posterior efferent artery 

 discharges into the epibranchial artery of the next following gill. 



There are thus four pairs of epibranchial arteries belonging to 

 branchial arches 1 — 4, i.e., formed from the dorsal portions of the 

 aortic arches of those branchiomeres. 



The first efferent artery — that of the hyoidean demibranch — 

 discharges into the first epibranchial artery, i.e., into the aortic arch 

 of the next succeeding branchiomere. 



