ANATOMY OF THE ENOPLA. 43 



The essential character or archetype of a Nemertean may be thus described :— A soft vermi- 

 form body, covered with cilia, and furnished with a thick glandular cutis, beneath which the 

 body-wall is composed of several strong, specially disposed muscular layers. Through the centre 

 of the body-cavity (and entirely beneath the nerve-commissures in front) passes the digestive 

 canal, which has two well marked divisions, an oral aperture anteriorly, and an anal posteriorly, 

 and is richly ciliated throughout. The nervous system consists of two conspicuous cephalic 

 ganglia, united by a double commissure, and giving off posteriorly a large lateral nerve-trunk, 

 which passes backwards on each side to the tail. The circulatory system is composed of a series 

 of closed contractile vessels. Along the median line of the dorsum lies a special muscular sheath, 

 containing a complicated proboscis, and a highly organized corpuscular fluid, both the sheath and 

 the proboscis passing between the commissures of the ganglia in front. The sexual organs are 

 in the form of sacs, placed between the muscular wall of the body and the digestive canal. 



I. — Anatomy of the Enopla. 

 1. Cutaneous System. 



The body of every example of the order is universally covered with cilia, the motion of which 

 may be very well observed in some of the larger forms by placing them in good light under a 

 lens. The proboscidian aperture, the mouth, and the tip of the tail, are generally furnished 

 with longer cilia, The ciliary motion is most active in the cephalic furrows of this group. 



In Jmphiporus lactifloreus the skin is somewhat opaque, and presents a cellular, or cellulo- 

 granular appearance (Plate X, fig. 6), the entire field being definitely covered with glandular cells, 

 and the reddish pigment, when present, grouped in irregular granular masses. I have not been 

 able to demonstrate the cuticle as a separate structure, on account of the softness and delicacy 

 of the tissues. On removing a portion of skin from a living specimen, and placing it under 

 moderate pressure, it presents the aspect of a series of ovate or spathulate cells (Plate X, fig. 5), 

 which contain soft and minutely granular contents, interspersed with large, clear masses of mucous 

 or gelatinous matter, having a similar figure, the latter becoming more abundant as the pressure 

 increases. There are also numerous pigment- and other granules scattered over the field. 

 Changes, however, rapidly ensue under pressure, and the contents of the cuticular spaces or 

 areolae pass rapidly to the nearest free border, and there accumulate as mucous and granular 

 circular masses (Plate X, fig. 1 a,b). A transparent gelatinous basis-substance, having a reticulated 

 aspect, remains after the extrusion of the foregoing elements from the skin. 



When a transverse section is made of the integument, after hardening in spirit and 

 mounting in chloride of calcium, the appearance (Plate X, fig. 4) is as follows : — In rapidly prepared 

 and newly fitted specimens, a structureless mucous film is sometimes observed to separate from the 

 exterior of the skin, as indicated by the double outline at the edge of the figure. Chloride of calcium 

 dissolves this ; and it has not been seen in those hardened in chromic acid. This is not an epiderm, 

 but only an exudation of transparent mucus, and it is also observed in the living animal under 

 pressure. The areolar cutis (a) is now much altered, and streaked perpendicularly, an appear- 

 ance due to the collapsed condition of the spaces, the contents of which to a greater or less degree 



