Haswett—Ox an apparently New Type of the Platyhelminthes. 155 
no vibratile cilia in any part. The cuticle and epidermis are, taken together, only 
about ‘003mm. in thickness—the epidermis taking up more than half of this. The 
epidermis resembles that of Zemnocephala in being nucleated, but not divided into 
cells—the nuclei being about ‘02mm. apart on an average. Pore-canals and clear 
spaces are recognisable in the epidermis as in that of Zemnocephala. Of the presence 
of a basement-membrane I am uncertain; appearances in some sections would seem 
to point to its presence; but the smallness of the object renders the determination of 
this and other points in its minute structure doubly difficult. An external circular 
and internal longitudinal layer of muscular fibres underlie the integument, but I have 
not seen any trace of the intermediate diagonal layer present in Zemmnocephala. 
Numerous dorsi-ventral bundles of muscular fibres traverse the parenchyma. 
The duets of the rhabdite-forming glands for the most part pass into the 
tentacles; but some of them reach the exterior in the interspaces between these 
appendages. 
LV.—Auimentary CANAL. 
The most remarkable feature of Actznodactylus, revealed by an examination of 
living specimens, is the presence of a proboscis (Pl. xvz. fig. 2) capable of being retracted 
within the cavity of the mouth. In only one specimen did I find this organ fully 
protruded; and, but for the observation of this specimen, I should have entirely 
overlooked it, as its character is not readily recognisable in my series of sections. 
Having once seen it, however, I afterwards succeeded in finding two or three 
specimens in which i€ could be seen in the act of being imperfectly extruded and 
then withdrawn. 
When fully extended this remarkable organ passed out beyond the margin of 
the body—equalling in length probably about one-third of the total length of the 
animal. It is of about the same thickness as the tentacles, but, unlike the latter, 
extremely sensitive and contractile. At its extremity is a pin-shaped stylet. When 
it was retracted I could find no trace of it either in living specimens examined under 
a slight pressure or in stained specimens; it appeared to vanish completely within 
the muscular pharynx, and more successfully prepared specimens will be required 
before its relation to the latter can be determined. 
The pharynx (fig. 4) is comparable to that of Zemmnocephala. Enclosing it 
externally, as in a sort of sheath, is a thin layer of transversely arranged muscular 
fibres. Within this the radial fibres, which are stronger than in the 7emnocephalee, 
take their origin, running inwards to the internal lining membrane. Running among 
the outer ends of the radial fibres is an outer stratum of longitudinal fibres, and among 
the inner ends an inner stratum—both being of considerable thickness. Internal to 
