Thalassema papìllosum (Delle Chiaje), a for^ottea Echiuroid Gephyrean. 435 



occupied positions about 2 mm apart, and about 5 mm from the 

 anterior end of the body. 



Colour. The preserved specimen has lost all traces of its ori- 

 ginal colour, and has adopted that dull yellowish white hue charac- 

 terist|c of specimens which have been for a long time in alcohol. 

 Mercüliano's sketch shows the colour of the living animai. The 

 papilla? are whitish in the preserved animai, as also in this coloured 

 drawing (fig. Ij. 



Integument. The whole skin is covered with papillse (fig. 5), 

 which cannot be said to have a regulär arrangement, although in 

 places they show a tendency to form transverse rows. They are 

 of very different sizes, and the smaller ones occupy the grooves 

 and Valleys between the larger. Posteriorly the integument is some- 

 what thickened, the papilhe become flattened and more confluent, 

 forming irregulär rings; 1 have observed the sanie tendency in 

 Thalasserna neptiml and giyas. The skin is thinner in the middle 

 of the body, in the preserved example it was here quite transparent. 

 Macroscopically the skin and musculature present the sanie structure 

 as in T. neptuni and EcJdurus, the skin more especially resembling 

 that of the latter worm in the greater concentration of the glands 

 on the papilhe. We find an epidermis, a well developed fibrillar 

 cutis, and three muscular layers. viz. au outer layer of circular 

 muscles, a longitudinal muscular coat, which is b}" far the thickest 

 of the three, and a very thin layer of internal oblique muscles. The 

 longitudinal musculature is not divided into separate bundles, but 

 fornis a continuous sheet, as in T. neptuni and gigas. 



The longitudinal ridge of muscle fibves, which in T. neptuni 

 Supports the nerve cord, is not present, the nervous system resting 

 directly on the oblique musculature. 



Hooks. Although the functional hooks had been lost, I found 

 fully developed »Ersatzborsten« in the skin. These are but slightly 

 curved (fig. 2), the free hooked part is rather widened out and 

 spear-head shaped when seen from the dorsal or ventral surface 

 (fig. 3). The musculature of the hooks is very weak (fig. 6 1i), in 

 comparison to the same structure in other Echiuroids; I cannot find 

 any transverse muscle band conuecting the hooks of the two sides 

 with oue another. Seen from inside in the dissected worm, the 

 apparatus appears to consist of the two little papillìe, in whicli tlie 

 hooks are developed, with a few weak muscular threads attaching 



29* 



