SCIENCE- G OS SIP. 



199 



head, and from the commoner species, S. mntlous, 

 by spines on the carapace. It is rare, one only 

 being found in water from Bollis Hill, that yielded 

 many individuals of seventeen different species. 

 The mouth is at the extremity of the head. In 

 Hudson and Gosse no antennae are figured, but I 

 am positive they exist, as later I found a number 

 in a ditch that drained into the Arun at Pul- 

 borough, Sussex, and made a very careful examina- 

 tion. 



Mastigocerca carinata is an interesting form, as 

 apparently it has only one toe, but rudiments of 

 others can be seen at the base. There are 

 antennae, which are difficult to make out, as they 

 are obscured by the cilia. It is to be found in 

 most of the places I have mentioned. 



Distyla flexilis I have only dipped once, when I 

 found some specimens in water from the azalea 

 house of the Botanical Gardens, London. It 

 resembles Monostyla mollis in many respects, but 



is easily distinguished by the two toes. They are, 

 like the Diaschiza, on the border line of the 

 loricated and illoricated free-swimmers. 



It has never been my good fortune to capture 

 Pedalion miruvv, whose discovery by Dr. Hudson 

 at Clifton in 1871 led to the formation of the 

 fourth sub-order. 



The study of rotifera has one disadvantage : it 

 is only the picture of your capture that is of much 

 practical use. There are methods of mounting 

 them, and these methods are not difficult, but 

 require much patience and care. They must be 

 placed in fluid and consequently in cells, and 

 this prevents examination with high powers. To 

 once fall under the spell of the wheel-bearers 

 is to remain convinced that their study is 

 the most delightful of all work with the micro- 

 scope. 



90 Belsize Road, 



South Hampstead, London. 



BUTTEEFLIES OF THE PALAEAECTIC KECMON, 



By Henry Charles Lang, M.D., M.E.C.S., L.R.C.P. Lond., F.E.S. 



{Continued from page 173.) 



Genus 16. COLIAS Fab. 



"OUTTERFLIES of moderate size. Wings with 

 •*-* the margins entire. Sub-costal nervure of 

 f.w. four-branched, the first given off before the 

 end of the cell, the second at the end of the cell or 

 external to it, the third and fourth bifurcating at 

 the apex of the wing. Hind wings always rounded 

 and without any angular projections. Ground 

 colour of wings yellow, varying in different species 

 from pale greenish to deep orange. Hind margins 

 always more or less bordered with black, at least 

 on the f.w. ; a black discoidal spot is always present 

 on f.w., except in one or two species. H.w. with a 

 conspicuous light discoidal spot, varying above 

 from orange to white, and of pearly white beneath, 

 generally surrounded by a reddish circle ; cilia 

 generally red. Antennae red in colour, short, and 

 rather thick, swelling into a club at the extremity. 

 Head of moderate size, eyes naked and tolerably 

 prominent. Palpi close together and compressed. 

 Thorax rather short. Legs generally red. Abdomen 

 moderately stout, and not reaching to anal angle 

 of h.w. 



The females are larger than the males, and 

 generally of a lighter colour ; the marginal border 

 is wider but less defined, and is spotted with yellow, 

 with one or two exceptions, even in those species 

 where the border is unspotted in the male. The 

 females of those species whose wings are normally 

 deep yellow or orange are liable to a dimorphism 

 in which the wings have the ground colour nearly 

 white. In this particular they greatly assimilate 



to what is seen in both sexes of the species of the 

 light-coloured group. This is familiar to British 

 collectors in the case of C. ednsa, var. helice, which 

 greatly resembles C. hyale. It has been thought by 

 some that this may be a reversion to a primitive 

 coloration, in fact to the original Pierid type. In 

 several instances, however, the principle is reversed, 

 as in some forms of a remarkable species, C. nv\scoit\, 

 in which the male has the light and the female is 

 of a yellow or orange colour. 



It is evident, then, that in the grouping of this 

 genus we must adopt the Horatian saying, " nimium 

 ne crede colori." Because a species happens to 

 have orange-coloured wings, it does not follow that 

 its affinities are necessarily with all orange-coloured 

 species. On the other hand, the genus Colias, as 

 commonly understood, forms a very natural group, 

 and to my mind those who would break it up into 

 several parts err in departing from that simplicity 

 which should be aimed at in all zoological classifi- 

 cation. If we take some of those species which 

 apparently are widely divergent, such as C. 

 sagartia, C. christopM, C. regia, C. wis7wtti, and 

 place them side by side, we shall not find one good 

 zoological character by which we are justified in 

 establishing any new genera ; although in colour- 

 ing they differ greatly. 



To go further than the character of mere colora- 

 tion we may take the pattern of the wing-markings, 

 but even here there are not sufficient grounds for 

 the division of the genus, because, as mentioned 

 above, the difference in character is really only 

 confined to one sex. In those species where the 



