HEEPYLLOBIUS ARCTICUS. 
405 
having mandibles, maxillae and maxillipeds, while the females 
of the Herpyllobiidge are entirely without appendages. The 
description of the males is at fault, for the adult male of 
Herpyllobius and Rliizorhina is limbless and degraded 
and cannot be said to possess mouth parts, while the male 
Choniostomatid is highly developed and has well-formed 
mouth-parts. 
It therefore seems best to retain the two as separate 
families, equivalent to the Chondracanthidm, the Lernaco- 
podidje and others. 
It might be of intei’est at this juncture to make some 
comparison between the Herpyllobiidge and the Rhizocephala, 
as each may be considered the most degraded form of the 
Copepoda and Cirripedia respectively. In both the adult 
female consists of two parts, one inside and one outside 
the host, the outside portion containing the reproductive 
system, whilst the part inside the host forms a root system 
for absorbing nutriment and conveying it to the external 
part. Some analogy might also be traced between the 
chitinous ring of the Rhizocephala and ihe chitinous hold-fast 
of Herpyllobius. There is of course a great difference in 
the method of infection: Sacculina,, for instance, obtains 
entrance into the body of the host as a larva, and undergoes 
metamorphosis as an endo-parasite, the adult being evagi- 
nated at maturity; while Herpyl lobius fixes itself to the 
outside of the host, probably at an early larval stage, and, if 
it is true that a protective membrane is formed by the worm, 
remains as an ecto-parasite throughout life. 
The Rhizocephala are as a rule hermaphrodite, thus differing 
from the unisexual Herpyllobiidm, but this is not always the 
case, for G. Smitld has found in the mantle cavity of 
Duplorbio what ajipear to be extremely degraded, but still 
functional males. In the ordinary individual no testes are 
found, as is also the case in Sylon, but in the latter no male 
individuals are known. 
' Smith, G., “ Rliizoceiihala,’’ ‘Fauna uiid Flora des Golfes von 
Neapel.,' Monogr. xxix, 1906. 
