July 11, 1903.] 



SCIENCE. 



65 



clear to all the real nature of the subject under 

 consideration. 



W. F. Ganong. 



THE EUROPEAN POND-SNAIL. 



To THE Editor of Science: It may prove 

 of interest to some of your readers, inter- 

 ested in geographical distribution and its 

 problems, to learn that there is a well estab- 

 lished colony of the European pond-snail 

 Limncea auricularia Linnseus in Flatbush 

 (Brooklyn). So far as I am informed this is 

 the only occurrence in America of the well- 

 known 'wide-mouthed mud shell' as it is 

 called in England. The colony is well estab- 

 lished, a number of individuals having been 

 collected that were over an inch in length and 

 correspondingly broad. They feed on pond- 

 lily leaves, destroying the epidermis on the 

 under side almost completely. They were no 

 doubt introduced through accident on water 

 plants, since the pond contains several well- 

 known European hydrophytes. Inasmuch as 

 the visits of water birds to this pond may 

 lead to the young shells being carried away 

 to. stock other ponds, the occurrence of this- 

 species should be recorded. 



B. Ellsworth Call. 



Brooklyn, June 28, 1902. 



TEXT-BOOKS. 



The evolution of educational methods in 

 this country is interestingly set forth by 

 President Plarper in 'The Trend of Univer- 

 sity and College Education in the United 

 States' {North American Eevieiu, April, 1902) 

 and the university of the future is portrayed 

 as centering about the library. Professor 

 Harper names two centers for the university 

 — the library and the laboratory; but for 

 present purposes the laboratory may be re- 

 garded as the workshop in which are tested 

 the 'receipts' of the text-books, so that the 

 laboratory may in a broad sense be taken as 

 an annex to the library. 



In a university library to-day the books are 

 so numerous as to require special training or 

 assistance to find and use their information 

 to best advantage. Books of course are writ- 

 ten from many standpoints and for many 



purposes, from scholastic erudition to the 

 juere passing of an idle hour, and wide is the 

 range between the needs of the specialist and 

 those of 'that delightfully vague person, the 

 intelligent reader,' as Mr. Haddon puts it in 

 his introduction to 'The Study of Man.' 



As text-books have been the outgrowth of 

 the needs of schools and colleges they reflect 

 in extent and method the needs and limita- 

 tions set by the requirements of each case. 

 And since these requirements differed 

 widely in different institutions, the number 

 of text-books in each subject is large and their 

 treatment varied. 



The chief peculiarity of a text-book is 

 brought about by the fact that it has been 

 prepared for use, not in imparting knowledge, 

 but in the training of the student mind. Its 

 method of presentation is therefore frequently 

 such as to require rather the maximum than 

 the minimum of mental effort to master its 

 contents. 



The second limitation to an ordinary text- 

 book, as felt by one who wants only to learn 

 facts, is that set by the length of time given 

 that study in some particular school or college 

 or grade of schools. Hence the ground is 

 covered sometimes quite incompletely, and 

 quite often a limited view is presented in a 

 way most valuable for use in mind-training, 

 but with important topics omitted wholly 

 rather than a less detailed but more complete' 

 outline of the subject. 



A third limitation is set by the omission 

 of much detailed 'elementary' information 

 imperative to a full understanding of the 

 subject, and assumed either as already known 

 or that it will be (but too often is not) im- 

 parted by the intelligent teacher. This criti- 

 cism of the teacher is fortunately becoming 

 less pointed as the science of teaching is 

 being learned and put into practice. 



There exists however to-day a large class 

 of would-be pupils who by force of circum- 

 stances must be self-instructed. They are 

 mostly tied down by the necessity of earning 

 a living for themselves and usually for others. 

 Their minds may or may not be trained but 

 they want to learn the known facts and their 



