SCIENCE-GOSSIP. 



137 



according to its nutritious or innutritious value will 

 produce large or small specimens ; but size alone 

 is not a specific character. It generates no new 

 modification of an existent organ. Sexual selection 

 is, in Lepidoptera, I believe, practically an un- 

 known quantity, and probably in some other 

 families of organized beings the supposed action 

 in this direction is much overrated. I fail, 

 entirely, to see how either isolation or the laws of 

 growth can originate a new structure, or modify 

 an existent one per se, although both forces are 

 valuable for the development of a modification, 

 once it has taken place. 



Utility of Specific Characters. 



It must be evident to anyone who will logically 

 consider the subject that, if the survival of the 

 fittest be the one test by which species exist, and 

 that all species have been brought about by a 

 gradual and almost imperceptible transition from 

 other species, the change which takes place and 

 becomes fixed in the species, i.e. the specific 

 character, and which separates it from its immediate 

 ancestor, must be a change that will be useful to 

 the species. Therefore, the presence of useless 

 specific characters, so-called, is more likely to be 

 due to our failure to understand their use, rather 

 than to any likelihood of their actual uselessness. 



In no case that occurs to me do any local races of 

 Lepidoptera exist in certain areas to the exclusion 

 of the type — except in the one case of Polyomviatus 

 astrarche var. artaxerxes, which is almost restricted 

 to certain localities in Scotland — without our 

 being able at once to show that they are adapta- 

 tions to environmental conditions, which make the 

 differentiating features of the utmost use to the 

 races exhibiting them. As these various local 

 races have assumed their racial characters for 

 purely utilitarian purposes, or are the result of 

 conditions under which the normal type would 

 cease to exist, so we may rest assured the char- 

 acters retained by various species have been 

 those which have remained useful to the species. 

 The characters which now distinguish them as 

 species most probably originated as racial pecu- 

 liarities because they were of use, and enabled 

 them to win in the struggle for existence which 

 they were obliged to wage against the various 

 species by which they were everywhere sur- 

 rounded. So far as an intimate study of our 

 lepidopterous fauna allows me to judge, I should 

 say that certainly every specific character is 

 or has been correlated with a character useful 

 to the species. 



Rayleigh Villa, 



Westcombe Hill, London, S.E. 



BRITISH INFUSORIA. 

 By E. H. J. Schuster, F.Z.S. 



(Continued from page no.) 

 Part IV. — Ciliata Heterotricha. 



TTHE order Heterotricha includes such forms as 

 are covered over with an even coating of cilia 

 and have besides a specially developed adoral band. 

 No distinction between the ciliation of the dorsal 

 and ventral surfaces can be observed. 



Family Bursariadae is characterized thus in 

 Mr. Saville Kent's " Manual of the Infusoria " 

 " Animalcules free-swimming ; persistent in shape 

 more or less oval, often considerably flattened 

 peristome field excavate, extending backwards 

 obliquely from the frontal border ; wide anteriorly ; 

 the oral aperture situated at the posterior and 

 narrowest confines of this region, frequently 

 followed by a well-developed pharyngeal passage ; 

 larger adoral cilia developed in a straight or 

 oblique line along the left hand margin of the 

 peristome only, not encircling the mouth in a 

 spiral manner ; anal aperture posteriorly situated ; 

 no undulating membrane." 



Bursaria tnmcatella Miiller. — The body of this 

 animal is persistent in shape, though flexible. It 

 is moderately long and bag-shaped. The ventral 

 surface is flattened down to a certain extent. The 



front end is slightly narrowed and truncated ; the 

 hinder end is usually broad and rounded, but may 

 be finished in a point. The principal characteristic 

 of the genus is the large and peculiar development 

 of the peristome field. This is triangular in shape, 

 with the base of the triangle directed forwards ; 

 the rather narrower gullet-like hinder portion 

 turns towards the left and leads towards the 

 mouth opening. A very narrow canal lies along 

 the right side of the peristome field and nearly the 

 whole way runs to the mouth. The left side of 

 the peristome field is fringed with an adoral band 

 composed of a number of flattened and mem- 

 branous cilia. This band is not continued off the 

 frontal border. The peristome field, except for 

 this, is unciliated and is not provided with an 

 undulating membrane. The body striation is 

 weak and spiral. The anus is probably at the 

 posterior extremity. The contractile vacuoles are 

 usually entirely passed over; they have been 

 observed by Clapareds, Lachmann and Biitschli 

 to be scattered over the whole body. The 

 macronucleus is long and band - shaped and 



F 3 



