27 



the thickest part of the proboscis, a transparent layer (fig. 42) which I regard, with Mastermax 

 (87, 2, pp. 342, 343), as nervous. 



The unpaired proboscis-cavity (fig. 42, b. c.') extends to the dorsal end of the buccal disc, 

 the epidermis passing round this edge as a fairly thick layer. A similar arrangement is seen 

 in the lateral edges of the dorsal half of the proboscis (figs, iii, 152). But ventrally to the 

 insertion of the proboscis-stalk, the anterior and posterior walls of the proboscis rapidly come 

 into contact, by the disappearance of the body-cavity in this region. The greater part of the 

 ventral lobe of the proboscis is accordingly formed of two layers of epidermis in close apposition 

 (fig. 42), the anterior wall consisting of a thicker epithelium, and the posterior wall of a very 

 thin layer which passes into the ventral epithelium of the proboscis-stalk, and so to the upper lip. 



In the region where the two epithelia of the proboscis are apposed, is invariably found 

 a characteristic line of pigment (figs. 3 — 7, p. b.), which has a brilliant red colour in the spirit- 

 specimens. This line forms a crescent, extending transversely across the ventral lobe, from edge 

 to edge, and with its concavity directed dorsally. The pigment can readily be seen in sections 

 (fig. 42), and it is clearly very resistent to the action of reagents. The pigment-line occurs very 

 early in the young buds, in which the enormous development of the buccal disc is one of the 

 most characteristic features (figs. 4, 9), and it is found in the males of C. sibogae (PI. VII, 

 figs. 72, 75, 76). 



In a well preserved specimen of C. dodecalophus (PI. XII, fig. 151), the pigment-line is 

 related to a special modification of the epidermis on its dorsal side. The cells immediately 

 adjoining the pigment are large protoplasmic cells, which have stained (with haematoxylin) less 

 intensely than other parts of the proboscis. These are followed by a group of numerous minute 

 nuclei in an area which is practically unstained. The deeply staining gland-cells of the anterior 

 epidermis then follow, at first sparingly and, near the bend of the ventral lobe, associated with 

 a considerable number of the minute nuclei already noticed. These become fewer in passing 

 dorsally, and the part of the anterior epidermis which is uniformly tinted in the figure is 

 constituted, up to about the reference-line b. c' ., almost entirely by the greatly elongated, densely 

 staining gland-cells Avhich e.xtend from the nervous layer to the free surface of the epidermis. 

 There are no gland-cells on the ventral side of the pigment-band. 



It is difficult to decide what may be the physiological significence of the pigment-band 

 and of its related cells. M'Intosh (87, pp. 27, 34) suggests that the pigmented oviducts may 

 be phosphorescent organs. No difference in colour can be noticed between the pigment in the 

 pigment-band of the proboscis and that of the oviducts, in the sections shewn in figs. 149 — 151, 

 and it is possible that there may be some relation between the functions of the two parts. 

 So far as the proboscis is concerned, it is conceivable that the function might be that of 

 vision, although the nerve-supply seems inadequate on that hypothesis, and it must further be 

 remembered that C. dodecalophtis is an abyssal form. But it seems ver)- improbable that the 

 oviducts, which have no distinct nerve-layer, can be used as visual organs. In the case of the 

 proboscis, the function of the pigment, whatever it may be, is probablj- associated with a 

 sensory function of some kind, as appears to be indicated by the presence of the numerous 

 cells wdth small nuclei which occur in the region of the bend of the proboscis in fig. 151. The 



