132 DR J. F. GEMMILL AND DR R. T. LEIPER 



description of the genus by leaving out reference to the very small number of eyes 

 characteristic of A. inconspicuus as apparently not of generic importance, and, by 

 substituting " under or close behind the pharyngeal sac " for " under the pharyngeal 

 sac " to indicate the position of the male apparatus. The first of these alterations is 

 required by A. stylostomoides, but in regard to the position of the male apparatus this 

 species conforms to the generic type as instituted by LANG. 



In the Euryleptid genus Stylostomum (3), mouth and male aperture open together 

 by a common antrum, and there is no median anterior gut root. LANG remarks that, 

 except for these two points, Stylostomum is almost exactly the counterpart of Aceros. 

 It is noteworthy therefore to find that in A. stylostomoides the male opening and the 

 mouth are so closely approximated that in certain states of contraction they may almost 

 be said to open together. 



The presence of a dorsal pore in A. stylostomoides is extremely interesting. The 

 pore canal passes downwards and forwards from the surface to the hinder part of the 

 main gut in the median line, and is clothed by epithelium agreeing in character with 

 the body epithelium except that its cells are provided with longer cilia, The basement 

 membrane is continued down the wall of the canal, and there are sphincter fibres at the 

 junction with the gut. 



Dorsal pores are described by LANG as occurring in Cycloporus, Yungia, and 

 probably also in Oligocladus (4). In Cycloporus they are very numerous and occur 

 near the body margin. Here the extremities of the ultimate gut branches become 

 enlarged to form vesicles which open on the dorsal surface, each by a tiny pore. 



In Yungia the pores occur on the dorsal surface at the places at which the 

 anastomosing gut branches meet. Here short diverticula from the branches end in 

 small vesicles opening by the pores. 



In Oligocladus the hindmost gut root on either side sends a diverticulum backwards 

 towards the dorsal surface in the middle line. These meet with one another and with a 

 mesial process from the main gut in a cell mass close under the dorsal body epithelium. 

 LANG was not able to find a pervious canal opening on the surface through the cell mass 

 in question, but he considers that in all probability this was due to contraction of 

 the tissues. 



The same author suggests that such pores may be considered as being homologous 

 with an anus, and that the numerous marginal pores in Cycloporus may be looked 

 upon as representing a primitive condition recalling the marginal excretory pores of 

 Coelenterates. 



In Yungia the pores, though fewer, are still numerous, and scattered over the 

 lateral parts of the dorsum ; while in Oligocladus there is only one pore, but it is 

 connected with the two last gut roots as well as with the main gut. A. stylostomoides 

 would complete the series, inasmuch as it has a single opening which is comparatively 

 large, and is connected only with the main gut. 



We are of opinion, however, that these pores, occurring as they do in a few 



(BOY. soc. EDIN. TRANS., VOL. XLV., 822.) 



