ON THE CLASSIFICATION OF THE ASCARIDAE. 
I.—THE SYSTEMATIC VALUE OF CERTAIN CHARACTERS OF THE 
ALIMENTARY CANAL. 
By H. A. BAYLIS, M.A. 
(With 1 Text-figure.) 
(Published by permission of the Trustees of the British Museum.) 
INTRODUCTION. 
The great French helminthologist, Dujardin, appears to have been the first 
to suggest a grouping of the genus “ Ascctris” according to the structure of 
the alimentary canal. As is, unhappily, only too well known to modern 
helminthologists, little attention was paid to internal structures by the earlier 
workers, whose numerous descriptions and classifications were based almost 
entirely upon external characters. It is now recognized that a natural system 
must be based on a survey of the whole structure of the animal, both external 
and internal, and a re-examination of many of the older species becomes 
extremely important. 
While some families of Nematodes have received considerable attention 
in recent years, and materials for a natural grouping are gradually accumu¬ 
lating, the Ascarid family seems to have been comparatively neglected, 
perhaps because of the extremely large number of species, to which every 
year still more are being added, and which seems to make it an almost 
hopeless task to reduce them to a natural, orderly and convenient systematic 
arrangement. Hall (1916), in the course of some introductory remarks to his 
valuable revision of the Nematodes of Rodents, has mentioned that in the 
index catalogue of the Zoological Division of the United States Bureau of 
Animal Industry something like a thousand species are enumerated under 
the generic name “ AscarisT Stossich (1896), in his monograph of the Linnean 
genus, mentions 218 species. Of course, many of the so-called “species” are 
no doubt synonyms, misdeterminations, or otherwise inadmissible; but, even 
allowing for this, the “genus” is intolerably unwieldy, and it is clearly time 
that effective steps were taken to split it up into smaller groups, if only for 
the sake of convenience. 
The process of splitting-up has been carried on in a desultory manner 
since Dujardin’s day, but has not, up to the present, led to any highly satis¬ 
factory results. No uniform system has been adopted by the various workers 
