the Genus Crassicauda. 411 
blue whale (Balenoptera musculus), and the worms were 
found with their caudal ends hanging freely into the urinary 
passage. In one case portions of the host’s tissues (penis) 
were forwarded, and show the head-ends of the worms still 
deeply embedded. ‘The tissue being very firm and muscular, 
and having been hardened in formalin, it has proved im- 
possible, as is usually the case, to extract the worms intact. 
They pursue a very tortuous course in the tissues, and are 
easily broken in the attempt to remove them. The present 
account, therefore, will necessarily be confined to the cha- 
racters of the posterior end. 
In a former paper (1916) the writer described what was 
believed to be the head of an example of Crassicauda crassi- 
cauda (Crepl.). Up to that time there was no definite ground 
for believing that the genus included more than one specics. 
In view, however, of certain considerations now to be set 
forth, there seems to be good reason for suspecting that two, 
and perhaps three, species of Crass¢cauda occur in whales. 
The original worms described by Creplin (1829) as Filaria 
crassicauda were comparatively small, 64 inches being given 
as the length of a complete male, 12 to 13 inches as that of a 
complete female. Creplin describes and figures a single 
spicule in the male. The greatest thickness (and this in one 
exceptionally thick female) was about 1 line [=about 2 mm.]. 
Leiper and Atkinson’ (1915), reporting on material con- 
tained in the ‘Terra Nova’ collection, which they had 
previously (1914) referred to C. er assicauda (inaking this the 
type of the new genus), remark that they were unable to find 
any spicules in the males, and conclude that they are absent. 
They also state that the material (which consisted only 
headless fragments) ineluded portions of both males and 
females of a length of 16 inches. 
A re-examination of the ‘ Terra Nova’ material, now in the 
British Museum, and its comparison with the new material 
from the South Shetlands, lead me to believe that the latter 
represents the true C. crassicauda, while Leiper and Atkinson’s 
determination of the former as belonging to Creplin’s species 
was erroneous. It is proposed, therefore, to regard the 
‘Terra Nova’ specimens as representing a new and larger 
species, which may be named Crassicauda boopis. It attains 
a thickness of between 3 and 4mm. Leiper and Atkinson 
unfortunately gave no figures of the worm. Figures of both 
forms are therefore given here for comparison. 
The material sent by Mr. Bennett includes fragments 
measuring up to about 16°56 cm. [=6$ inches] in length 
and not more than 2 mm. in thickness, ‘Tlie males have a 
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