255 
H. A. Baylis 
Section 4. “True Ascarids having a single pyloric caecum or appendix 
springing from the oesophagus, posteriorly, alongside of the intestine.” 
A single species, 
Host 
A. acus Bloch. The Pike (Esox). 
This resume of Dujardin’s system has been given because it seems to have 
been generally either forgotten or ignored by more recent workers, some of 
whom have actually created new genera for forms having exactly the charac¬ 
ters given by Dujardin for one or another of his Sections 2, 3 and 4, without 
mentioning the fact that Dujardin had already noticed them, and without 
comparing the new forms with those included in Dujardin’s groups. 
During recent years an attempt has been made by Railliet and Henry 
(1912) to group together all the Ascarids in which oesophageal or intestinal 
diverticula occur. They thus created the subfamily Heterocheilinae, which 
they have subsequently (1915) shown a desire to elevate to the rank of a 
family, Heterocheilidae. More recently still, Gedoelst (1916) has given a 
dichotomous table of forms referred by him to the Heterocheilinae (ap¬ 
parently not accepting the group as of family rank) to which he has added 
a new genus, Dujardinia , for the reception of Ascaris helicina Molin. The 
table is based on the following features, which are here given in the supposed 
order of importance: 
(1) Presence or absence of intestinal and oesophageal caeca. 
(2) Presence or absence of interlabia. 
(3) Presence or absence of dentigerous ridges. 
In the course of the following remarks it will be necessary to inquire 
whether this subfamily (or family) can be regarded as a natural group, and to 
see, if possible, to what extent the presence or absence of caeca connected 
with the alimentary canal provides a sound basis for classification. 
Data derived from a re-examination of species. 
With the idea of obtaining some more definite knowledge of the occurrence 
of these modifications of structure in the alimentary canal, and of the re¬ 
lationships, if any, between the forms in which they are found, a number 
of species of Ascarids available in the British Museum have been re-examined 
expressly from this point of view, note being also taken of the presence or 
absence of interlabia and dentigerous ridges—points usually assumed to be 
of systematic value. The list of species so examined at present is very limited, 
but the results already appear to the writer to indicate that the occurrence of 
such structures is more widespread among the Ascaridae than has hitherto 
been realised, and that it may have a very important bearing upon the 
ultimate systematic grouping of these forms. 
Parasitology xn 
17 
