72 Annals of the South African Museum. 



form a trough. Sections through such organs are shown in figs. 25 

 and 26. 



In its histological structure the skin surrounding the basal organ 

 (as well as that of other parts of the body) closely resembles that of 

 P. capensis, as already described by Balfour (1883), — that is to say, 

 each individual epithelial cell, whether it forms part of a primary 

 papilla or belongs to the surface between the papillae, is produced 

 distally, so that its free end forms a convex or conical " secondary " 

 papilla (or " scale," as Bouvier calls them; figs. 21-23). Each cell 

 is again thickly covered with minute prickles on its exposed surface, 

 but it does not terminate in a spine, except in the case of some of 

 those on the larger primary papillae. The transition to the epithelium 

 of the basal organs (as at x, figs. 21 and 22) is quite abrupt ; the 

 prickles on the surface as well as the scales suddenly disappear, 

 being replaced by a smooth thin cuticula upon the surface of which 

 I could not discover any sculpturing whatever. In sections, however, 

 this cuticula often appears wrinkled (as in fig. 23) or even partially 

 detached from its matrix owing to the contraction of the latter. The 

 cells of the matrix do not show any noticeable difference in the size 

 or in the appearance of their nuclei, but their protoplasm appears 

 striated, often even fibrous (fig. 22), much more distinctly so, in fact, 

 than that of the surrounding echinate epithelium, in which the 

 vacuolar or foam structure is more evident. 



I failed to notice any peritoneal lining to the coxal organs, whose 

 base, therefore, appears to be in direct contact with the blood in the 

 leg cavity, and blood corpuscles {be) may generally be seen in the 

 neighbourhood. 



Isolated muscular strands are attached to the bases of some of the 

 matrix cells in the peripheral parts of the coxal organs and especially 

 also to the ectodermal cells immediately adjoining these organs 

 These muscles undoubtedly serve for the purpose of invaginating the 

 whole organ into the cavity of the leg, from whence it may be 

 protruded again by blood pressure. 



From fig. 23 it will be seen that not only the smooth epithelium of 

 the coxal organ, but also a considerable portion of the surrounding 

 echinate skin is invaginated to form the deep groove at the base of 

 the legs. 



Peripatus.— Coxal organs in various states of expansion and 

 retraction may be observed in most of the legs in the American 

 species of Peripatus, and the variability of their appearance has 

 already been frequently alluded to by various authors (Gaffron, 1883, 

 Bell, 1883, Sedgwick, 1888&, &c.). 



