J46 



NATURE 



[yan. 28, 1875 



it. Is it not probable that the whole secret consists in 

 the ants continually using for food those seeds which 

 begin to germinate, and that there always remain many 

 seeds whose germination is delayed ? 



The remainder of the volume is devoted to Trap-door 

 Spiders, many new species of which have been discovered, 

 and much curious information obtained as to their habits. 

 The spiders and their nests are illustrated by figures 

 which are models of accuracy, and far surpass in delicacy 

 and finish those of the first volume, good as those were. 

 There are some interesting remarks about the British 

 Nest-making Spider {Atypns siilzcri), which has very 

 rarely been observed, but which, now attention is called 

 to the subject, will no doubt be found to occur plentifully 

 in the South of England. The new double-tubed and 

 double-doored nest now first described is the perfection 

 ot insect architecture ; and being constructed by a single 

 insect is far more indicative of intelligence, mechanical 

 skill, and reasoning power, than the habitations of ants or 

 bees. 



This volume is a striking example of the way in which 

 the most confirmed invalids may employ and enjoy them- 

 selves ; of the marvellous interest that attaches to the 

 minute observation of the habits of many of the lower 

 animals ; and of the vast field for discovery that is still 

 open to observers. It will long remain a standard work 

 on the subject of which it treats, as well as a vvorthy 

 memento of the enthusiastic and amiable naturalist whose 

 early departure from among us will be so widely deplored. 



A. R. W. 



THE UNIONID^ 

 Observations on the >>eniis Unio, together -with descriptions 

 of new spceies in the family Unionida. By Isaac Lea, 

 LL.D. (Philadelphia, 410.) 



ALTHOUGH no date of publication is given, the last 

 paper contained in this volume appears to have 

 been read on the 3rd of February, 1S74. It is a goodly 

 volume of seventy-four pages, and twenty-two beautiful 

 plates. 



The number of this volume (xiii.) shows the extent to 

 which the octogenarian, but still indefatigable author, 

 Dr. Lea, has prosecuted his favourite study. He tells 

 us in the Introduction : " In my twelfth volume I 

 mentioned the number of North American species 

 (Unionida;) then known to be 772. By adding sixty 

 to these, we have the number 832 species." And he 

 remarks that " these do not by any means constitute the 

 whole number of existing species ; many of the smaller 

 streams falling into our large rivers have not been ex- 

 plored, and these when well searched will unquestionably 

 produce new forms of this numerous and interesting 

 family." 



Now it seems to us that the little word " forms " thus 

 innocently used must disarm every conchologist of that 

 weapon of criticism (species-making) with which Dr. Lea 

 has been so often and so mercilessly assailed on this side 

 of the Atlantic. Substitute "form" for "species," and 

 what is there to prevent the European Unionidre attaining 

 a more respectable position as regards number than they 

 do at present ? In Great Britain we can show only five 

 species, besides sixteen named and well-marked varieties. 



In Germany, according to Kreglinger, there are fifteen 

 species (including some of our varieties), and twenty-nine 

 named varieties. The number could be increased almost 

 ad infinitum by reckoning every distinct form from each 

 river, stream, lake, canal, and pond in which the Unionidas 

 are found ; and we should lose one test of specific differ- 

 ence, which consists of ignoring all variation ot shape 

 caused by habitat, and which induces us to believe that 

 undoubted species are those that live together without 

 any intermingling or gradation. But whether all the 

 North American Unionida; are called "species," or 

 " varieties," or " forms," Natural^iHistory and Conchology 

 in particular are under a great obligation to Dr. Lea for 

 his admirable works. One, perhaps not the least, merit 

 is his symmetrical method of description, the characters 

 of every species being given in the same relative order, 

 so that they can be readily compared and the differences 

 between the several species more easily ascertained. 

 This is certainly important in his case ; because some of 

 the figures on the same plates bear a rather suspicious 

 resemblance, e.g. those of Unio globatus and subglobatns, 

 U. tuscuinbicnsis and radiosus, U. criidus and pattinoides, 

 U. yadkincnsis and conasaugacnsis, U. ampins and inso- 

 lidi/s, U. rostelliim and cxactitns, besides U. subparallelus 

 and basalis. The above-named species are compared 

 by the author, not with each other, but with different 

 species. 



Another reflection occurs to us on the perusal of this 

 work ; and that is as to the division of labour. A uni- 

 versal naturalist is now an extinct animal ; and the region 

 of biology becomes every day more and more subdivided 

 into separate fields of investigation. Thus, in the MoUusca 

 Mr. Davidson restricts himself to the Brachiopoda, Dr. 

 Lea to the Unionida;, and Dr. L. Pfeiffer to the Pulmono- 

 branchia. Every other department of zoology, as well as 

 of botany, has its own votaries for different orders and 

 even families ; and it is in this way that knowledge is at 

 present advanced, not by some great Corypha;us, but by 

 many less-gifted persons who have the opportunities and 

 inclination 



" To labour and effect one thing specially." 



OUR BOOK SHELF 



La Vie; Physiologic Hnmaine, appliqu'ee d l hygiene et 

 a la Midccine. Par le Dr. Gustave le Bon. (Paris : 

 J. Rothschild, 1874.) 

 Most authors compose their works first, leaving the pre- 

 face until the last thing, in order that they may appreciate 

 the full intluence of their detailed study when making the 

 generalisations with which they feel bound to start their 

 volume. We hj.ve no reason to think that the author of 

 the work under notice is any exception to this rule. In 

 the nine hundred or so pages of his book he explains in 

 a clear and very intelligible manner many of the most 

 important facts and theories of the science of physiology; 

 in some parts introducing improved methods of illus- 

 tration, in others not quite recognising the most recent 

 advances which have been made, even by his own 

 countrymen. Particular stress is laid, throughout the 

 work, on the bearing of the points discussed on eveiyday 

 life, on hygiene, and on pathology ; in all of which the 

 author, from his experience in the routine of practice and 

 the recent Franco-German war, in which he was engaged 

 in active ambulance service, is able to speak with autho- 

 rity. There are two other points in which the work is 



