124 Mr. H. A. Bay lis 07i 



found only in the Ca])e Verde Islands. The material proved 

 to include two forms of approximately the same size, but 

 easily distinguisluible, even when viewed in S[)irit under a 

 low magnification, by the strikingly different proportional 

 lengths of the oesophagus (fig. 1, A and B). In one form, of 

 which both sexes are present in large numbers, the oesophagus 

 is very long and slender. This is undoubtedly the species 

 described under the name of Oxyuris paronai by von Linstow 

 (1893), from the same host-species. The other form has a 

 short and relatively stout oesophagus, and, though the speci- 

 mens number some hundreds, all are females. 



von Ijinstow's original specimens of Oxyuris j^cironai are 

 in the British Museum, and on examining them with a view 

 to placing beyond doubt the determination of the new material, 

 it at once became apparent that the same two forms were 

 again present. Further investigation, in this case also, failed 

 ti) reveal any males of the form with short oesophagus, thougli 

 males of the otiier form were present in ))lenty. It appears, 

 therefore, that the association of tliese two forms in Alacru- 

 scincus is of common occurrence. It was even suspected for 

 a time that this might be a case of very marked dimorphism 

 limited to the female sex. Closer investigation, however, 

 lends more support to the view that the forms are specifically, 

 or even generically, distinct. The females of the form with 

 short oesophagus are fully mature, and contain ova, and it 

 seems possible that they are parthenogenetic, or represent a 

 parthenogenetic generation. 



Oxyuris paronai appears to be referable to the genus 

 Paracis, as recently defined by Ruilliet and Henry (1916), of 

 which the genotype is P. longicollis (Schneider, 1866) from 

 the tortoise. A comparison of the figures of the tails of males 

 given by Schneider (1866, pi. vii. fig. 8) and by v. Linstow 

 (1893, pi. vii. figs. 18, 19) is sufficient to demonstrate this. 

 Both forns have a blunt, finger-like, caudal appendage in the 

 male, with a pair of papillae close to the tip ; a single spicule, 

 and an accessory piece which forms a median pi'ojection 

 behind the cloaca ; and a group of paired papillae surrounding 

 the cloacal aperture. They also agree in the great relative 

 length of the ceso))hagus. 



I'he structure of the mouth in P. paronai, though difficult 

 to make out owing to the very small size of the head, seems 

 to offer characters which may prove to be of generic rather 

 than specific importance. The aperture of the mouth, as 

 v. Linstow indicates, is surrounded by a delicate, membranous, 

 triangular, funnel-shaped apparatus. This, however, is fully 



