75 



the central ncrvDUs system, which hc has more recently admittcd (99, 2, jjp. 359, 361) not to be 

 a blood-space, bat to have the peculiar rclation to the vascular system possessed by the peri- 

 cardium of Balanoglossus, as described by Spengel; (II) a vessel proceeding backwards from 

 the pericardium in the dorsal mesentery of the collar, bifurcating at the antcrior border of the 

 dorsal diverticulum of the pharynx, and reuniting behind that cavity to form (III) a vessel lying 

 in the mesenter)- between the jjharynx and the rectum, connected with (IV) a system of sinuses 

 round the stomach; (V) vessels to the ovaries; (VI) a ventral vessel, passing down the anterior 

 side of the body and stalk ; and (\'II) a vessel on the dorsal side of the body-cavity of each 

 arm, giving oft" a branch to each tentacle. In a later paper (98, 2, p. 512, figs. 12, 13) Mastermax 

 gives figures shewing that the ovaries are supplied from the dorsal blood-vessel, and in the same 

 memoir (p. 513) he describes a "dorsal" and "ventral" vessel in the stalk, which he states to 

 be '^direct continuations of the similar vessels in the trunk". 



Still more recently (03, p. 719), Masterman gives a more elaborate account of the 

 vascular system of the "central complex", or region between the buccal shield and the mouth. 

 The general result of this paper is to indicate an almost complete resemblance between Balano- 

 glossus and Cephalodiscus in the details of the vascular system of the proboscis-stalk. The blood- 

 sinus which runs in the dorsal collar-mesentery comnumicates with the "heart", which is related 

 to the pericardium in the same way as in Balanoglossus. Glomeruli are described, both on 

 the anterior wall of the pericardium and on the "ventral blood-sinus" which lies beneath the 

 notochord. There is a blood-sinus coming from the dorsal wall of the proboscis to the anterior 

 glomerulus; and vessels passing from the arms are said to enter the dorsal sinus at the level 

 of the posterior end of the pericardium. The ventral sinus e.xtends backwards as far as the 

 base of the notochord, where it divides into two vessels which pass round the mouth. 



I have no wish to dispute the accuracy of most of Masterman's statements with regard 

 to the vascular system, although on one or two points I cannot agree with him. But I must 

 admit that I have not been able to satisfy myself of the existence of all the vessels which 

 he describes. 



The question really turns on the interpretation which should be given to certain spaces 

 in Cephalodiscus which may be vascular and on the other hand may be merely artefacts. There 

 is of course no tracé of colour in the blood of the preserved specimens, nor are any corpuscles 

 to be seen. Certain evidence of the presence of a coagulum inside the "vessels" can only rarely 

 be obtained. There are, however, in Cephalodiscus, numerous spaces between the limiting mem- 

 branes of adjacent coelomic spaces, or between the membrane and the ectoderm or endoderm ; 

 and these spaces may be vascular in nature. But when one remembers the fact that the material 

 which is at present forthcoming was not preserved by rehned histological methods, and further 

 that there is evidence of great contraction in certain parts of the animal, I think it is well to 

 be cautious in assuming that all the spaces in question are vascular. 



I am none the less inclined to think that most of Masterman's account is substantially 

 accurate. I cannot agree with his statement referred to above that the "dorsal" and "ventral" 

 vessels of the stalk are "direct continuations" of the "similar vessels in the trunk". This apjaears 



