66 ANATOMY OF THE ENOPLA. 



arrangement of the stylet-apparatus, as, in addition to the forward position of the marginal 

 sacs, the central stylet and its surroundings are placed in his second oesophageal cavity, 

 that is, in our reservoir; and his figure bears out his description, representing, moreover, the 

 organ as placed at the commencement of the posterior channel. The species is easily identified 

 by the position of the marginal stylet-sacs and other peculiarities, and there is certainly no such 

 abnormality of the central apparatus or alteration of type as noted and figured by this naturalist. 



In Tetrastemma Bobertiance the glands of the anterior division give the organ a faint pinkish 

 colour. The middle region has two stylet-sacs of the usual structure, and a central apparatus 

 (fig. 5) which differs from the ordinary form in Tetrastemma in being somewhat enlarged 

 anteriorly. The stylets (Plate XIV, fig. 10, a and b) are short. and stout, similar in shape to 

 those of T. melanocephala, though decidedly smaller. Thus, while distinctions in the size and 

 shape of these organs are valuable, they should not be too much relied on for specific separation. 

 The external circlet of glands does not proceed further backwards than the posterior third of the 

 basal apparatus of the central stylet. 



The general arrangement of the proboscis in Tetrastemma Candida agrees with that in 

 A. lactifloreus. If under examination the ejaculatory duct is placed on the left of the central 

 apparatus (Plate XIII, fig. 5), an explanation is obtained of the mistake into which M. Claparede 

 had fallen in his description of the region in Tetrastemma varicolor (Erst, (the figure, however, 

 appears to me to be very like that of T. Candida). The central stylet and its apparatus have been 

 slightly pressed backwards, so that the radiating fibres which sling them have been brought out 

 distinctly, and sometimes a faint line of demarcation is seen on the right (in such a position) — 

 simulating the presence of a separation; but numerous fibres are prolonged past this, and, 

 moreover, a slight contraction or change of position obliterates the line, while the curved or 

 radiating fibres are rendered more evident. On the left the only boundary to the supposed 

 distinct coat around the wedge-shaped investment is the wall of the ejaculatory duct. The basal 

 apparatus of the central stylet in this species (T Candida) has rather more shape than in 

 T. melanocepliala, and is proportionally more elongated (Plate XIII, fig. 6). I thought a slight 

 difference could be detected between this species and T. dorsalis (Plate XIII, fig. 8, c), for the stylet 

 in T. Candida is generally shorter in proportion to the length of the basal structure. Consider- 

 able variations exist in the size of the several stylets in T Candida, independently of the magni- 

 tude of the animal, a fact perhaps the less surprising when the reproduction of the tube is remem- 

 bered ; but the greater size is generally diagnostic when compared with the three following 

 species. The central and marginal stylets (Plate XIV, figs. 6 and 7) nearly agree in length. In a 

 developing or recently repaired central apparatus (Plate XI, fig. 13) the basal portion is thinned off 

 anteriorly from contraction of the parietes, and the difference in size between its stylet and one 

 from the marginal sac of the same animal (Plate XI, fig. 14) is marked. 



The stylet-region in Tetrastemma dorsalis is closely allied to that in the former species. The 

 stylets, however, are on the whole more slender, and the central longer in proportion to its basal 

 apparatus (Plate XIII, fig. 8). The same may be said of T vermicula (Plate XIII, fig. 4). 



The shape of the central apparatus in Tetrastemma flavida is characteristic (Plate XIII, 

 fig. 9, c), the stylet being more slender than in the two former species, longer in proportion to 

 the basal apparatus, and having the margins of the latter nearly straight. The comparatively large 

 size of the glands of the reservoir in Tetrastemma is well illustrated in this species, where they 

 form very prominent structures with granular contents, and more closely allied to those in the 



