28 



sensory function claimed for the anterior epidermis of the ventral lobe may be connected with 

 the deposition of the gelatinous layers which constitute the coenoecium. The lobe is obviously 

 very mobile, as is indicated by the varying positions which it occupies in the preserved zooids. 

 Since, however, neither the musculature of the proboscis nor the anterior body-cavity extends 

 into it, its movements would seem to depend on protoplasmic contractions of the epidermis. 



It is not improbable that the nerve-layer shewn at the base of the thicker parts of 

 the anterior epidermis may extend as a thinner stratum into the ventral lobe, though I have 

 not definitely proved that this is the case. 



The ventral extremity of the anterior body-cavity extends, below the base of the 

 notochord, as far as the upper lip (figs. 37, 42, 1835 ?/./.), which occurs immediately in front 

 of the pharyngeal diverticulum {div.), from which the notochord originates (fig. 181). The 

 relations of this ventral part of the proboscis-cavity to the upper lip and to the notochord 

 suggest those of Balanoglossus, in which the corresponding part of the coelom gives rise to 

 the median part of the "nuchal skeleton" or "proboscis-skeleton", and in certain species to the 

 structure described by Spengel (93, p. 175; 03, p. 280) as the "blumenkohlahnliches Organ", 

 a structure to which Willey has given the name of "racemose organ" (99, 2, pp. 229, 260). 



In certain positions of the proboscis (figs. 43 — 46) the ventral epidermis of that organ, 

 in front of the mouth, forms the roof of the passage which encircles the proboscis-stalk, and 

 conveys the food from the arms to the mouth. In passing from the mouth outwards this food- 

 channel gradually ascends the proboscis-stalk, and becomes the deep groove (figs. 151 — 147, 

 f.c.r.\ fig. 155, f.c.r., f.c.i.) which is bounded in front by the posterior epidermis of the 

 proboscis, and behind by the thicker epidermis of the anterior side of the arm-base. The thin 

 posterior and ventral epidermis of the proboscis thus has an important part to play in helping 

 to define the cavity in which the food must pass from the arms to the mouth. The dorsal 

 epidermis of the proboscis immediately in front of the end of the collar contains a strong 

 nerve-layer (figs. 35, 37, 42) which is a direct continuation of the central nervous system. 



The more important structures directly connected with the proboscis-cavity, or contained 

 in it, are the notochord, the pericardium, the proboscis-pores, the glomerulus, and the muscles. 

 Of these the notochord may conveniently be treated in Section XI dealing with the alimentary 

 canal, while the muscles are described in Section XII. 



Pericardium and proboscis-pores. 



The pericardium was first figured by M.\sterman (97, 2, figs. 2, 3, 14, etc.) who described 

 it, however, as a blood-cavity. This account was criticized by me in a note (97) in which I 

 contended that the pericardium (= "heart-vesicle") has the same relations as in Balanoglossus; 

 and Masterman has more recently (99, 2; 03, p. 719) accepted this view. 



The pericardium of Cephalodisais closely resembles that of Balanoglossus. It may readily 

 be found, in all the species, in contact with the dorsal wall of the proboscis, immediately in 

 front of the ti]) of the notochord, and between the ends of the anterior dorsal horns of the 

 collar-cavity. It appears to form a completely closed vesicle (PI. XI, fig. 138; PI. XIII, fig. 181) 

 the posterior wall of which is invaginated into the lumen of the organ to form a space which, 



