NOTOMASTUS LATERICEUS. 279 



Between the dorsal and the ventral bristles of the first region is a pore with palpocils, 

 the opening of the lateral organ. In the second region the pore occupies the space which 

 separates the ventral and dorsal tori (De St. Joseph). Further, a little behind the double 

 median torus, is, on each side, in six to eleven of the first segments of second region, the 

 papilla for the genital opening. In finely developed forms a distinct conical papilla is 

 present at the inner dorsal edge of the great torus near the genital papilla. 



The proboscis is extruded as a large button-shaped organ covered with minute 

 papillae. The stomach occupies the anterior region, whilst the intestine commences at 

 the second region, and the gut is filled with muddy debris. The plasma is colourless, but 

 the discs, which float in the coelomic space, are reddish-brown, and are 0*010 mm. to 

 0*014 mm. in diameter (De St. Joseph). 



The difference in tissue between the anterior and the succeeding region is sufficiently 

 demonstrated by the condition of the large and fine examples tossed on the shores at the 

 West Sands at St. Andrews, where almost every specimen consists only of this (anterior) 

 region, with perhaps here and there traces of a few segments of the second region. The 

 differences in the muscularity of the parts sufficiently explain this feature. Whether the 

 result is due to abrasion during the storm or violence in situ in the sand is an open 

 question, but probably the former is the explanation, the less coherent posterior region 

 disintegrating under the strain. 



Reproduction. — In the first segment of the second region and in the six to eleven 

 following are the openings for the issue of the genital elements on papillae on the ventral 

 surface. In some cases these are not visible, probably because the animal is unripe (De St. 

 Joseph). Langerhans mentions that the ova are red or brownish-red. The whitish sperms 

 give a dappled aspect to some males (Plate XCII, fig. 2). 



A variety of this species (Gapitella D) was dredged off Cape Finisterre at a depth of 

 eighty-one fathoms in the ' Porcupine ' Expedition of 1870. It (Plate XCVIII, fig. 21) is 

 distinguished by its smaller size, but the bristles and hooks (Plate CVII, figs. 13 and 13 b) 

 are similar. 



Eisig established the genus Tremomastus from the presence of genital sacs in the 

 second region. De St. Joseph doubts whether these are constant. Sars gives twenty 

 pairs in N. latericeus, Horst eleven pairs, and De St. Joseph seven to twelve. 



De St. Joseph found numerous Loxosomae parasitic on an example. Those at St. 

 Andrews are free from them. The experienced French author was of opinion that the 

 Gapitella rubicund a of Kef erstein l is this species, and there is nothing in Keferstein's de- 

 scription and figures to contra-indicate this view except the absence of the median furrow 

 in the anterior segments and the corresponding modification at the bases of the bristle- 

 bundles. But in examples of Notomastus rubicundus, Kef erstein, kindly sent from 

 Plymouth by Dr. Allen, a distinct median furrow is visible, and though the specimens are 

 all small, a similar arrangement of the bases of the bristles appears to be present, and also 

 faint traces of reticulation of the surface, as indeed Keferstein's figure (fig. 7) indicates. 

 It would therefore seem that this form is a variety (and in the Plymouth examples a young 

 stage) of Notomastus latericeus. The hooks and bristles are identical, as are also the 

 posterior segments and tail. 



1 ' Zeitschr. f. wiss. Zool./ Bd. xii, p. 123, Taf. xi, figs. 7—18, 1862. 



