110 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



Some parasitic forms, however, are and must remain ineradicable, for the reason 

 that food-fish are their final hosts, and the intermediate hosts are a necessary food of 

 the fish. For example* the intermediate hosts of certain echiuorhynchi which infest 

 some species of fish have been found to be certain small Crustacea, as Echinorhynchus 

 proteus, which has Gammarus pulex for an intermediate host; while the gasteropoda are 

 almost universally infested with cercaria?, the larval stage of the trematoda. 



V. 



Some lines of investigation which suggest themselves as of importance to the 

 science of helminthology will now be briefly treated. By way of introduction to this 

 part of the subject in hand I wish to be indulged in a short digression. It often hap- 

 pens that the working helmiuthologist wishes to identify the host of some form which 

 he has found. In order to do this in a great many orders of animals he is obliged to 

 waste a great deal of time in rummaging through the ordinary books with which 

 every good general library is supplied, and even then too often with the result that 

 the species, not necessarily an uncommon one, can not be identified. There is certainly 

 need among working naturalists for compilations which will enable one to do in zoology 

 what he can do in botany with the aid of such works as Gray's Manual. 



It is surely contrary to the spirit of true science that the acquisition of correct 

 systematic knowledge in zoology should be limited to the vicinity of large libraries, 

 or that there should be an hierarchy of specialists to whom we must go in order to 

 learn the systematic position of every form that is at all unusual. Morphological and 

 embryological investigations are of the greatest importance, and in the end must be 

 depended on in testing and revising the work of the systematist; but is there not 

 danger that in all this anxiety about cell division, panmyxia, the trausmissibility of 

 acquired characters, the meaning of sex, etc., to which our most prominent biologists 

 are giving time and talents, a generation of students is being produced who are 

 attempting to work out problems in this country for which we are not ready? At 

 least, while there are so many groups of animals practically untouched and so much 

 to be done in the way of studying animals in their bionomic relations, it is certainly 

 not unfitting to speak a word occasionally to incite to the study of nature as she is in 

 nature and not wholly as she is in the laboratory. I am ready to confess for myself 

 in this regard that I sin daily, for I preside as best I can over a laboratory where, to 

 borrow an idea from my highly esteemed and most excellent friend Prof. S. A. Forbes, 

 nature is boiled in corrosive sublimate and fried in paraffin before she is given 

 serious study. 



For the orders which are comprised in the study ordinarily designated by the term 

 helminthology — viz, Cestoda, Trematoda, Acanthocephala and Nematoda — there is call 

 for much preliminary work before such a compilation as I have been pleading for in 

 other orders can be made anything like exhaustive; and this because of the little 

 pioneer work that has been done. 



In my own work I have been compelled, by stress of circumstances, to confine my 

 collections almost entirely to the vacation months of July and August and to rather 

 limited localities; but even here 1 have found material so abundant and so much of it 

 new that I have kept thus far, for the most part, along the somewhat antiquated but 

 still necessary path of systematic work. 





