SCIENCE-GOSSIP. 



Mergui Archipelago, but as this has never been 

 confirmed it may be assumed that the collector, 

 the Rev. J. Benjamin, made a mistake as to the 

 locality. Mr. W. T. Blanford gives also the 

 following localities : Moulmain and Tenasserim (in 

 " British Burma Gazetteer," 1879, i. p. 709). 



Plectopylis anguina (figs. 79a-/), from Tavoy, Burma, 

 was described by Dr. Gould in the " Proceedings 

 of the Boston Natural History Society," ii. (1847), 

 p. 218 ; and it was figured in Hanley and Theo- 

 bald's " Conchologia Indica," t. 13, f. 7. By 

 some authorities this species has been considered 

 identical with P. achatina. It appears, however, 

 to be perfectly distinct. The shell is sinistral, much 

 flattened, discoid, varying in colour from corneous 

 to dark chestnut ; below it is usually paler and 

 flammulated with dark chestnut ; it is finely striated 

 and decussated by microscopic spiral lines. The 

 spire is depressed, the suture linear. There are five 

 and a-half regularly coiled whorls, which increase 

 slowly and gradually ; they are a little flattened 

 above and a little rounded below. The last whorl 

 is slightly angulated at the periphery ; it widens 

 rather suddenly at the aperture, and is deeply 

 deflected in front, and somewhat constricted behind 

 the peristome. The umbilicus is extremejy shallow ; 

 in a specimen in my collection it is only 1-5 milli- 

 metre in depth. The aperture is nearly horizontal, 

 cordate ; the peristome is livid or pale brown, a 

 little thickened and much reflexed. A sinuous 

 raised ridge on the parietal wall at the aperture 

 connects the margins of the peristome ; at the 

 junctions above and below, however, there are 

 slight notches. The armature is similar in most 



respects to that of P. repercussa, but it is less solid 

 and heavy, the lower arm of the bifurcation on the 

 parietal wall is longer than the upper, and the thin 

 free horizontal fold near the lower suture is not 

 united to the ridge at the aperture and does not 

 proceed beyond the lower arm of the bifurcation, as it 

 does in P. repercussa. The upper fold of the 

 palatal armature is much shorter than in 

 P. repercussa, terminating posteriorly at the same 

 point as the shorter upper arm of the parietal 

 bifurcation ; the second and fifth horizontal palatal 

 folds are much shorter anteriorly than in P. 

 repercussa ; while the vertical palatal plate (the 

 fourth) is broader, but less stout and less inclined 

 towards the aperture than is the case in that species. 

 The specimen shown in figs. jqd and e is from 

 Moulmain, and is in my collection. It measures : 

 major diameter, 28 millimetres ; minor diameter, 

 22 millimetres ; altitude, 7-5 millimetres. Mr. Blan- 

 ford has also recorded the species from Tenasserim 

 ("British Burma Gazetteer" (1879), i. p. 709), 

 while Mr. Nevill mentions Kuengan ("Hand-list," 

 p. 72). Mr. Ponsonby possesses two specimens from 

 Sgwagakin, Salween Valley, measuring 25 milli- 

 metres in diameter. Figs, jga-c are reproduced 

 from photographs of Dr. Gould's type specimens 

 in the New York State Museum. Dr. Bagg has 

 supplied the following notes respecting them : 

 "Helix anguina, Gould. Catalogue No., 251; 

 original No., A 558. The shell is somewhat 

 banded by brownish and white alternating, but not 

 in all specimens." Fig. 79/ shows the posterior 

 aspect of the parietal and palatal armatures. 



(To be continued.) 



ORIGIN OF SPECIES IN INSECTS. 

 By J. W. Tutt, F.E.S. 



(Continued from p. 44.) 



On the Origin of Species. 

 A GREAT change in the environment of a species, 

 "^ locally, produces in that district a local race. 

 It matters not whether the change be one of 

 climate, food-supply, introduction of new enemies, 

 or geological change, so long as it is sufficiently 

 marked to affect the species injuriously under the 

 new conditions. Given these conditions, and the 

 injury will result in extermination, unless some 

 structural or functional modification be developed 

 in the species which will enable it to combat the 

 disabilities under which it now lives, and, in time, 

 to succeed under the new conditions. We have 

 already seen that a recent change in the environ- 

 ment of certain Lepidoptera has resulted in the 

 development of a maximum of black scales, so that 

 the colour of the insect may respond to its new 

 environment. We have also seen that this change 



of colour is simply a change in the proportion of 

 the black scales (always present in the species) 

 developed. The change then must take place by 

 the modification of the different variable factors 

 that play around what we may term the " mean " 

 of any structural part of the insect. It must be 

 evident that from these variable factors alone 

 can utility obtain the materials that it moulds 

 into those lines which will fit the species to its 

 new environment. Survival of the fittest in the 

 required direction or directions goes on year by 

 year, and thus the species is maintained under the 

 new conditions. 



Little further insight is needed to see that more 

 than one modification may be necessary, and that 

 under a complex series of change divergent races 

 might be formed, each specially suited for success 

 in different directions ; whilst the original type of 





