884 MR. W. WOODLAND ON THE [ISTov. 27, 



the base of the tail, i. e. towards the cloaca, this supi'a-neural vein 

 breaks up first into two smaller veins situated to the side of bvit 

 still above the nerve-cord, and still more anteriorly into a number 

 of very small veins which soon become lost between the constitvient 

 masses of the myotomes. In the adult the vein (which is very 

 obvious) lies immediately ventral to the elastic ligament men- 

 tioned above ; in the embryo examined this ligament was not at 

 that stage developed (fig. 8, PI. LVIII., represents a section 



Text-fie-. 138 



Centrophorus calceus. 



Diagram of section of posterior caudal vertebra, showing position of tlie 



supra-nenral vein (S-V.); E.L., elastic ligament. 



through an anterior caudal vertebra, hence the supra-neural vein 

 is not shown there). The formation of this supra-neural vein by 

 the fusion of numei'ous latei'al veins is a forcible illustration of 

 the production of median vessels by flexion of the body which I 

 have elsew^here '^'^ insisted upon. I have not been able to discover 

 a similar supra-neural vein in the Common Dogfish, and apparently 

 there was not one present in a lai-ge specimen of EcMnorMniis 

 spinos'us which was examined foi- me at Plymouth. 



EXPLANATION OF THE PLATES. 



Plate LVII. 



Centrojthorus calceus. 



Fig. 1, Cloacal resjion. L.A.P., left abdominal pore ; OD., oviduct ; R., rectum ; 

 R.A., opening of rectum into cloaca ; R.A.P., enlarged right abdominal 

 pore ; R.G., rectal gland ; R.O.A., right oviducal aperture ; U.P., urinary 

 papilla. 

 2. Scales from dorsal and ventral surfaces of body. B.P., basal plate; 

 T.S., tritid spine. 



32 " On a New Mode of Persistence of the Posterior Cardinal Vein in the Frog 

 {Bana temporaria) : with a Suggestion as to the Phylogenetic Origin of the Post- 

 caval Vein." Zool. Anzeig. Bd. xxviii. (23) 1905. 



