404 
KATHLEEN HADDON. 
skin of the host and there expands into a collar-like hold-fast, 
from which there depends an ohlong or irregularly -shaped 
body, which is homologous with the tubes of Rhizorhina 
and has the same function of supplying nourishment to the 
external body. Levinsen (9) has found that Saccopsis and 
Bradophila have stalks, but he has found no expanded body 
at the end of it in the body of the host; Hansen (4), however, 
is of the opinion that some tubes must run into the body of 
the host, otherwise it is difficult to see how the parasites get 
their food. 
A comparison between the two best-known j^enera 
of the family HerpyllobiidEe, K hizorh i n a and Herpyllo- 
bius, shows important differences in the stalk of the female, 
as mentioned above, and also in the male. In both forms the 
larva fastens itself to the female, after Avhich the tissues of 
the larva contract, thus forming a sac-like adult, without 
visible internal organs except the gonads and their efferent 
ducts. In Rhizorhina the male remains entirely inside its 
larval skin, pushing its generative ducts out through a hole 
in front of the mouth of the dead case. In Herpyllobius 
the skin of the larva bursts and the male is fastened by the 
anterior end, the generative ducts proceeding through the 
split pjroduced by the bursting of the larval skin. 
VI. Affinities of Group. 
Giard and Bonnier (2) regarded the Herpyllobiidte as 
closely resembling the Choniostomatidse, for although they 
considered the females too degenerate to admit of com- 
parison, they believed that the males, especially the larval 
males, strongly resembled one another both in the mouth 
parts and in the position of the genei'ative opening. For 
these reasons they proposed to make a new order, Sphaero- 
nellidae, containing two subdivisions, the Hei ])yllobiin£e and 
the Choniostomatinae. 
Hansen (4), however, points out that there are structural 
differences in the two groups that render such a classification 
unsatisfactory. The female Chouiostoniatid is less degenerate, 
