57 



In the account which Mastermax (98, 2, p. 507) has given of the mouth and i)liarynx, 

 the food-grooves of the arms are said to be continuous with certain groovcs on the inner side 

 of the wall of the pharxnx. The grooves unite, two by two, so as to form a system of three 

 lateral "oral grooves" which enter the mouth on each side (figs. i, 2) \ These proceed posteriorly 

 and dorsally and finally form a large niedian dorsal hyperpharyngeal groove (figs. 4 — 9). The 

 gill-slits are indlcated as two ventro-lateral channels even in sections immediately behind the 

 mouth (figs. 2, 3), while further back their walls are seen to be continuous dorsally with the 

 "pleurochords", and to be formed of the same sort of tissue (fig. 8). The alimentary portion 

 of the pharynx commences as a median ventral groove (fig. 4) between the two gill-pouches, 

 and soon fornis a large section of the pharynx lying ventrally to these structures (figs. 5 — 9). 

 Figs. 90 — 92 shew that the dorsal diverticulum of the pharynx has 4 grooves, two dorsal and 

 two ventral (or, as I prefer to call them, posterior and anterior, respectively), the section of 

 the lumen being hence quadrangular. The four grooves are directly continuous with the lumen 

 of the notochord (Masterm.\n"s "subneural gland"). The two "dorsal" grooves pass down the 

 dorsal wall of the pharvnx and are traceable as far as the commencement of the oesophagus, 

 being situated on the median side of the pleurochordal outgrowths, in the region of those 

 organs (figs. 93 — 99). The "ventral" grooves of the pharyngeal diverticulum pass down the 

 sides of the mouth (fig. 93, z'.o".), ventrally to which they unite, in course of time, to form the 

 large median alimentary part of the pharynx. This again can be traced to the beginning of the 

 oesophagus; and the lumen of the posterior end of the pharynx is thus triradiate in section 

 (two dorsal grooves and one ventral groove). By the median union of the two "ventral" grooves 

 of the pharyngeal diverticulum a "peri-pharyngeal band" is constituted. This, if I understand 

 Masterman correctly, is joined b)- the oral grooves on the anterior side of the pharyngeal 

 diverticulum. 



Masterman recog-nises that the grooves which he has described are too small to allow 

 the supposition that the water-currents carrying the food pass along them, and he has suggested 

 that they direct the flow of a secretion of mucus by which the food-particles are entangled 

 and are thus prevented from being washed out through the gill-slits. Here I think he is right, 

 although he guards himself from expressing any very definite opinion as to the direction of the 

 flow of mucus. The notochord is, however, regarded as a mucus-secreting organ, while the 

 pleurochords serve partly as a channel through which any excess of water which has passed to 

 the posterior end of the pharynx travels forwards in order to issue at the gill-slits. This view 

 is illustrated by Masterman's diagrammatic fig. 100. 



It is obvious from a consideration of the sagittal sections figured in Plate IV that the 

 relations of the mouth depend greatly on the position which the anterior end of the animal, and 

 in particular the proboscis, happens to occup\-. Thus in C. levinseni, the pharyngeal diverticulum 

 in fig. 33 has its opening directed towards the anterior side of the animal, while in fig. 34 it 

 is directed ventrallv- In the one case, a series of sections transverse to the long axis of the 



i) These references relate to the figures given in Plates I and V of Masterman's paper. Figs. i — 9 are from a transverse 

 series of the whole animal, passing therefore transverselj- through the beginning of the alimentary canal, and longitudinally through the 

 main part of the pharynx. Figs. 90 — 99 are transverse to the long axis of the animal, and are therefore what I term "froutal"'. 



SlIiOGA-EXPEDITIE XXVI /J/V. ° 



