150 PROF, G. B. HOWES AND W. RIDEWOOD ON [Mar. 6, 



adults of certain species, may or may not arise by confluence or 

 suppression of individual segments {cf. fig. 8) ; future research must 

 decide this question. 



There remain two most important questions. 1, If the segmented 

 condition be the more primitive, may not the whole pre-hallux repre- 

 sent a shortened-up digit? and 2, May not this supposed sixth digit 

 represent a lost ray of the ichthyopterygium ? 



In Nannophrys, Phijlloniedusa (fig. 19 a), Rhombophryne, and 

 especially in some species of Hyla, the pre-hallux has quite a digiti- 

 form aspect, comparing, at first sight, very favourably with the 

 reduced pollex of the fore limb, the homology of which with the 

 other digits nobody disputes {cf. Plate VIII. figs. 19 a & 20). 



That the pre-hallux may, in a sense, resemble the pollex is clear 

 from the preceding ; but it must not be forgotten that this resem- 

 blance is most marked in the specialized Tree-Frogs. Its segments^ 

 are, in the embryo, more digitiform than in the adult ; and taking all 

 facts into consideration, we incline to a belief in a preponderance 

 of the resemblances over the differences between this structure and 

 a normal digit. 



The second difficulty is not easily to be met. That the pre- 

 hallux takes on certain of the essential relationships of a digit is 

 beyond dispute. That it really represents one is another question. 



The tarsal of the pre-hallux is, in most cases, in definite articu- 

 lation with the head of the naviculare (cf. Pelodytes, fig. 13). In 

 many forms its second segment is the largest (ex. fig. '27); when 

 this is the case, that may be disposed parallel with the metatarsals, 

 in a manner strikingly suggestive of a serial homology (cf. Xenopus, 

 fig. 3, aud Pseudis, fig. 27). In Xenophrys, Hyla (figs. 1/ and 

 19), and other genera, this supposed metatarsal sends forwards (back- 

 wards in situ) a small retral lobe (*) ; in Ceratophrys (fig. 24) 

 this attains a considerable development, and in individuals of this 

 genus it may exceed in size the body of the segment from which it 

 takes its origin. 



Meckel (29) and Cuvier (15) held, and Born (3), Kehrer (24), 

 and others still hold the pre-hallux to be a sixth digit. Leydig 

 (25), attacking it from a totally different standpoint, argues to the 

 contrary. Gegenbaur at first took a similar view, holding (18) it to 

 be a secondary structure peculiar to the Anura, and his words are 

 echoed by Hofmann(2I); subsequently however to the publication 

 of Born's paper, Gegenbaur accepted that author's position, con- 

 fessing to the same in his well-known text-book. Finally, Born 

 asserts, in his latest paper (6, p. 61 ) *' TJbrigens bin ich jetzt geneigt 

 in der starken Variabilitat der Gebilde der sechsten Zehe . . . 

 nicht bloss mehr eine Eigenthiimlichkeit zu sehen, die derselbem 

 als rudimentarem Organ anhaftet, sondern ich sehe in der haufigen 

 Verschmelzuug ein Bestreben ein immer festeres Skelettstiick als 



^ Van Deen records (34) an instance in which, in Eana escidenta, these lay in 

 a line with the hallux and supported the web. His specimen was, unfor- 

 tunately, a monstrous one, with four hind legs. 



