MAKINE CRUSTACEANS. 453 



It may not be amiss to consider the fiicts brought out by an examination of these 

 varieties in their rehition to some theoretical considerations brought forward by Mr Borradaile 

 in an earlier part of this work (Vol. I. Pt. II. pp. 193 — 198 "Marine Crustaceans. I. On 

 Varieties "). 



1. It will have been noticed that, in cases where there is a sufficient number of any 

 given variety, the individuals representing this variety come, not from one definite locality, 

 but from different localities, a fact which bears out Mr Borradaile's statement, on p. 195, 

 that " there is no evidence of isolation such as is presupposed in the evolution of two or 

 more varieties simultaneously from a single species." 



2. The transition-scheme which I have given of the tumidus-glabrous series has been 

 arranged in two columns, arising out of the fact that two distinct lines of variation are 

 present in the series, one being due to the development of the anchor leading to the 

 formation of the submedian carinae, which is common to both the columns, the other being due 

 to the presence or absence of a spine to the median and submedian carinae, such spines being 

 present in first column (excepting var. acutus and smithii a.) and absent in the second. Now 

 if the relation of these spines to the carinae be examined, it will be found that, according 

 as the carinae are more tumid, the spines are less prominent ; thus, taking extreme instances, 

 it is seen that in var. smithii the median carina is almost sharp and has a strong spine, 

 but that in the analogous var. incipiens the carina is very tumid and without a spine. 

 Moreover, when, in var. glabrous, the carinae become more tumid, so as to produce eventually 

 what I have called above " term h" the spines entirely or nearly disappear (var. mutatus, how- 

 ever, appears as an exception to this rule), as also do the carinae and spines on the 6th 

 abdominal segment. Thus we find that the shape of the carinae and the development of the 

 spines can only be taken as constituting a single differentiating character, the two apparent 

 variations being, as Mr Borradaile has expressed it, in his footnote 2, to page 197, "coin- 

 cident." A similar fact has been already brought forward by myself in dealing with some 

 Malaysian Crustacea (Ann. Mag. Nat. Hist. (7) vi. 1900), where in dealing with Actaea pidchella 

 var. modesta (p. 251) I have said, " It is true that three distinctions are noticed, but these 

 three are really only one variation, the curvature of the dactyl and the gape of the fingers 

 being implied by the emargination of the finger-tips." I give this case as another illustration 

 of the point under consideration, and as helping to confirm, together with the present instance 

 of G. chiragra, the more theoretical opinions expressed so clearly by Mr Borradaile in his 

 footnote 2, p. 197 ; with which, I need hardly say, I find myself in entire agreement. 



3. In dealing with var. glabrous, it has been seen that great difficulty existed in separating 

 the intermediates between the two " terms " into definite gi'oups, and I have above also ex- 

 pressed my reasons for believing that we have in var. glabrous a Continuous Variation series; 

 the series being obtained, not fi'om one, but fi"om more than one locality. Now this fact 

 conflicts to a certain extent with some remarks made by Mr Borradaile on pp. 196 — 7 to 

 the effect that, where " well-characterised non-local varieties " exist, these varieties " are sundered 

 by well-marked gaps " ; and the writer adds, " In sorting fifty specimens of two varieties, there 

 would not, in my experience, be more than two or three whose position would be doubtful " 

 (see also footnote 1, p. 197). Now I do not deny the validity of Mr Borradaile's particular 

 facts, which are, of course, cases of Discontinuous Variation, but his remarks seem to imply 

 that, in all cases where we find well-characterised, non-local varieties, the variation will be 



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