ANATOMY OF THE ANOPLA. 95 



and A. F. Marion. In Borlasia kermapkroditica, Kef., the anterior genital sacs were full of sper- 

 matozoa, and the posterior of developing ova ; while in B. Kefersteinii, Mar., the sexual elements 

 appeared to be distributed throughout the whole length of the body, but whether alternately or 

 otherwise the author does not state. 



II. — Anatomy and Physiology of the Anopla. 



1. Cutaneous System. 



The skin in this group, of which Lineus gesserensis may be taken as the type of the majority, 

 is closely allied to that of the Enopla, though its structure is frequently rendered obscure by the 

 greater development of the pigment. The cilia are very active in the cephalic fissures, and it is 

 sometimes noticed that their motion is suspended and again resumed without evident cause. In 

 the living animal the cutis has a cellular aspect (Plate XVII, fig. 16), the cells or areolae measuring 

 about y^qq of an inch, and most distinctly seen towards the tip of the tail in the adult. Sometimes 

 a number of minute clear granules are placed over the larger cells, as shown at the lower third of 

 the figure. The pigment-cells and granules reach their greatest development anteriorly, and some 

 of the former contain very dark brownish-black pigment in circumscribed masses. The dorsal 

 pigment has in general a longitudinally streaked appearance (Plate XVII, fig. 15), a state probably 

 arising from the peculiar arrangement of the fibres of the external muscular layer hereafter to be 

 described. In some pale red specimens the coloration is due to a uniform impregnation of the cutis, 

 and the tint is much deeper than that of the ganglia, which are thus rendered conspicuous by their 

 pallor. Occasionally one or two pigment-cells of exceptionally large size are present anteriorly 

 (Plate XVII, fig. 18), each containing from one to three clear granules. 



In transverse sections, underneath the ciliated epidermis (c, Plate XVIII, fig. 4), a somewhat 

 thick layer (d), composed of granular cells and globules in areolae, occurs. Prom the facility with 

 which these contents escape, the drawings show the parts in a slightly altered condition. Beneath 

 is a pale structureless basement-layer (</), the presence of which in Cerebratulus had led Prof. 

 Keferstein into the error of supposing it to be a layer of circular muscular fibres ; but an attentive 

 examination of that genus, as well as the present, demonstrates that, while one may be deceived 

 if only transverse cuts are made, no doubt can exist in longitudinal sections. This point may 

 readily be settled without reference to the more explicit, because larger, condition of the parts in 

 Lineus marinus. A thick compound layer is next encountered in L. gesserensis, consisting 

 externally of pigment-granules and cuticular globules (d"), and internally of a series of powerful 

 longitudinal muscular fibres (<?). Under a low power, indeed, this compound layer in transverse 

 section appears as one, the pigment and other cells, and the ends of the muscular fibres, pre- 

 senting a similar aspect. The amount of pigment varies, of course, in different specimens, and is 

 always much more developed dorsally than ventrally. Towards the anterior end of the animal 

 this coat (d") becomes thicker, and its reticulations more distinctly marked. Fine longitudinal 

 sections of the snout from above downwards show superficially a series of very beautiful reticu- 

 lations of a somewhat regular aspect (Plate XVIII, fig. 10, *), the chief interstitial bands having 



