To6 



NATURE 



[September 22, 192 1 



tion of births was not enforced in England until 

 1875, ^"<^ it is probable that for many years later 

 both birth and death registration were imperfect 

 and irregular in Ireland, especially in its remote 

 parts. 



It would be more satisfactory, as supporting 

 natural changes in fertility, if other trustworthy 

 instances could be quoted. True, Dr. Brownlee's 

 figures for Geneva are quoted showing a decline of 

 more than 40 per cent, in the birth-rate between the 

 beginning of the eighteenth century and the early 

 nineteenth century ; but these figures, like some 

 other international rates for prolonged periods, 

 can scarcely be said to favour the view that fluc- 

 tuations in the birth-rate (corrected for number 

 of marriages and age at marriage) occur natur- 

 ally. If they do occur naturally we must assume 

 that they are physiological in character, being 

 rhythmic variations in " germinal vitality " 

 (Brownlee), which have been compared to the 

 outbursts of infectivity, say, in the influenza organ- 

 ism, the cause of which is unknown to us, though 

 we express our ignorance by using Sydenham's 

 language of "epidemic influences." Mr. Yule 

 sees no reason " why man should be exempt from 

 analogous phenomena," but it is difficult to con- 

 ceive any analogy between variations in activity 

 of unicellular organisms and variations m 

 sexual activity of a complex mammalian. Nor are 

 we impressed by the suggestion of comparability 

 of such phenomena as plagues of field-mice or 

 plagues of locusts. These are more naturally 

 explained on the supposition that an excessive 

 death-rate has occurred among other creatures 

 which would have maintained the balance of 

 Nature; and it does not appear inappropriate to 

 refer to the old puzzle as to the relationship 

 between old maids, field-mice, bees, and the 

 clover crop. 



This last suggestion brings us to the most 

 valuable sectjon of Mr. Yule's paper. Whether 

 contraceptive measures or other causes, not being 

 arithmetical as explained above, have caused the 

 reduced birth-rate, how is the birth-rate related 

 to economic conditions? Mr. Yule is convinced 

 that the course of prices is closely related to the 

 trend of the marriage-rate and of fertility, though 

 he states that he is at a loss to suggest the precise 

 nature of the nexus. He regards the nexus as 

 economic, probably acting via psychology rather 

 than directly through physiology ; and he does 

 not believe that the nexus is wholly volitional, 

 acting through contraceptive measures or other- 

 wise. He regards migration, marriage-rate, and 

 NO. 2708, VOL. 108] 



fertility as only three forms of response to 

 demand for population. 



There we must leave this momentous problem. 

 It deser'ves even more study than it has hitherto 

 received. That economic circumstances, raising 

 the age for gainful employment and the like, 

 have had marked influence in lowering the birth- 

 rate is certain. That the desire for a higher 

 standard of comfort and for a more satisfactory 

 upbringing of a smaller family, not necessarily 

 selfish, has been a potent factor is equally with- 

 out doubt. Whether at the end of another 

 generation the differential birth-rate will, as 

 many fear, lower the standard of health and 

 intelligence is doubtful. The present writer 

 regards this fear as exaggerated. Talent 

 emerges in all social strata; but where large 

 families imply imperfectly nourished children and 

 a deficiency of parental care, they must neces- 

 sarily lower the average standard of health. Is 

 this occurring for a larger proportion of the total 

 population than in previous generations? Prob- 

 ably not. 



Indian Land Mollusca. 



The Fauna of British India, including Ceylon and 

 Burma: Mollusca.— 111. Land Operculates. 

 [Cyclophoridae, Truncatellidae, As'simineidae, 

 Helicinidae.) By G. K. Gude. Pp. xiv + 386. 

 (London : Taylor and Francis ; Calcutta : 

 Thacker, Spink, and Co. ; Bombay : Thacker 

 and Co., Ltd., 1921.) 355. 



AMONG the Indian land mollusca the family 

 Cyclophoridae especially attracts attention 

 by the beauty of form and variety in the shells. 

 The range is extensive, and their study began so 

 far back as 1849, when W. H. Benson, of the 

 Bengal Civil Service, and Capt. T. Hutton were 

 writing on the animal of Diplommatina. After 

 seventy years the above families are still very im- 

 perfectly understood, so little is known of the 

 animal which constructs the shell. I think I am 

 correct in saying the time had not arrived for 

 publishing a volume on these molluscs, for suflfi- 

 cient material had not been examined; in truth, 

 much has yet to be collected. It would be inter- 

 esting to know for this reason why Mr, Gude 

 was selected to do it, and the work then left to 

 all intents and purposes completely in his hands ; 

 why malacologists with knowledge of the subject 

 were not consulted ; and why the present 

 writer, with more than forty years' connec- 

 tion with these land operculates, both in the 

 field and in collections, was in complete 



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