46 ANATOMY OP THE ENOPLA. 



contents of the areolae having for the most part escaped. The aperture for the proboscis perforates 

 the tissues just at the ventral border of the tip. A remarkable interlacement of fibres, occupying 

 almost the entire cephalic region, occurs in front of the ganglia (Plate X, fig. 3). Powerful bands 

 (1) pass below both the buccal cavity and the tube for the proboscis, meet, and cross each 

 other in an oblique manner, making afterwards, by their divergence, extensive lateral con- 

 nections ; indeed, it will be observed that towards the inner muscular layer the fibres just 

 mentioned form a broad fan-shaped arrangement. Some (2) pass upwards by the side 

 of the central canal, and mingle with those descending from this region, while others (3) 

 curve downwards to the ventral wall. Those (4) meeting above the central canal intersect each 

 other obliquely in the middle line, so as to constitute a firm arch; and, besides, there are some 

 transverse fibres (5) which cross over the canal and spread out laterally. Another series 

 (6) slants downwards and inwards on each side of the cavity, and forms a firm junction 

 inferiorly. The arrangement of these bands and fibres is so intricate, that each seems to blend 

 with the other, and make a continuous anastomosis of contractile meshes. In addition to these 

 oblique and radiating fibres, a powerful longitudinal series is interwoven with them in a complex 

 manner, besides the denser grouping (e) at the margin (which indicates the inner muscular 

 coat of the body), and the glandular masses in the centre. It will be observed that the bands 

 which pass beneath the central canal are the most powerful, and offer a much greater resistance to 

 the bulging of the proboscis and its sheath than the superior fibres, so that in extrusion the organ 

 is mainly directed upwards (Plate X, fig. 8). The inferior commissure of the ganglia is thus some- 

 what protected by the arrangement of the fibres in front of it. The blood-vessel (Plate X, figs. 3 

 and 9, /) lies on each side in a sheltered angle between two series of fibres ; and its calibre would 

 not seem to be much interfered with except in extreme protrusion of the proboscis, though this is 

 not of much consequence in the economy of these worms. All the oblique or transverse fibres 

 are connected with the body-wall and the inner muscular layer, as are also the longitudinal at the 

 tip of the snout. This elaborate interlacement provides in the best possible manner for the varied 

 changes which the region undergoes during protrusion and retraction of the proboscis, and the 

 ordinary motions of a tactile and mobile, yet not too yielding snout. The arrangement of the 

 oblique and circular fibres around the longitudinal layer of the central canal must also act the part 

 of a constrictor, and adapt the cavity to its ever-varying calibre. On the whole, the stroma in 

 this group, from the greater predominance of cellular and granular elements, is less dense than in 

 Linens, and the interlacement of the fibres, though not more complex, is more beautiful, because 

 possessing greater distinctness and regularity. 



The posterior end of the body does not present this intricate arrangement, but the muscular 

 fibres blend together and close in the cavity, with the exception of the small and sometimes indis- 

 tinct opening of the great digestive chamber. The modes of fracture of these muscular coats in certain 

 of the Anvphiporidce in a sick and perishing condition are interesting, the animal being separated 

 into a number of beads, from the constriction and rupture of the body-wall at somewhat regular 

 intervals. 



In specimens of Amphiporus pidcher from which the cutaneous textures have been removed 

 by improper preservation, the muscular coating has a glistening aspect, and is marked by a con- 

 spicuous double row of genital pores along each side. This glistening appearance of the muscular 

 layer on removal of the cutaneous tissues is also seen in certain Plan arise. 



M. cle Quatrefages described the muscular coats both in Borlasia and Nemertes (especially 



