On an Australian Land Nemertine. 99 



frequently of a black appearance, owing doubtless to the 

 presence of air within it. Sometimes one meets with 

 abnormalities in the development of the stylets. One of 

 these is represented in Fig. 17 {a. '^it.), where several points 

 are attached to one head. Very often small shining globules 

 appear to be attached to the outer surface of the stylet just 

 in the constriction which marks off the head (Fig. 17a.) 



There can, I think, be little doubt that these calcareous 

 stylets originate, like sponge-spicules, in special mother cells. 

 Occasionally small granular cells (Fig. 17c.) may be detected 

 in the sacs containing the reserve stylets, and these 

 sometimes seem to bear already the beginning of a stylet 

 (Fig. 17, St. m. c.) 



I have not succeeded in finding any communication 

 between the reserve sacs and the lumen of the eversible 

 part of the proboscis, but probably theie is some communi- 

 cation as in other species. The structure of the central 

 stylet and the accessory ones appears to be identical, and 

 there can be rio doubt that the latter are destined to replace 

 the former when it is broken off or worn away, but the 

 manner in which they come to be inserted into the top of 

 the handle is to me a perfect mystery. 



When the proboscis is completely everted the central 

 stylet, of course, must project freely at its free end, and 

 doubtless it forms, with tlie poison, an efficient weapon of 

 offence or defence. 



The posterior half of the stylet-region is less complicated 

 in structure. It is a swollen, bulbous organ, with very 

 thick muscular walls, in which the muscle fibres do not 

 appear to be arranged in definite layers, but circular, 

 longitudinal and oblique or diagonal fibres occur more or 

 less mixed up together in a dense mass. Outside is the 

 usual low epithelium, very difficult to make out, and inside 

 is a large cavity (Fig. 1^, p. v.), the poison i-eservoir, which 

 is also lined "^ by a low and apparently non-glandular 

 epithelium, and communicates anteriorly, by means of the 

 poison canal, with the lumen of the eversible portion of the 

 proboscis, and posteriorly, by a short constricted canal, 

 with the lumen of the non-eversible portion. The latter 

 penetrates, with its own muscular coat, for a short distance 

 into the posterior part of the stylet region, as shown in 

 Figure 15. 



The non-eversible portion of the proboscis (Figs. 14, 15, 

 n. e. r.) is relatively thin-walled, and the muscular elements 



