HERPYLLOBIUS ARCI'ICUS. 
385 
Herpyllobius arcticus. 
By 
Kiitlileon Iladdoii. 
With Plate 22 and 4 Text-figures. 
Contents. 
I. Introduction 
II. Material . 
III. Anatomy 
A. The Female. 
1. External appearance 
2. Part embedded in the host 
3. Microscopical structure 
a. External jiart 
b. Stalk and root system 
B. The Male. 
IV. Relation of Parasite to Host 
V. Comparison with Allied Genera 
VI. Affinities of Group 
YII. Systematic 
YIII. Summary and Bibliography 
PAGE 
385 
388 
388 
388 
389 
392 
392 
397 
402 
403 
404 
400 
408 
I. Introduction. 
Among parasitic copepods Herpyllobius is remarkable 
for the extreme degeneracy attained by the adult male and 
female, both of which are entirely devoid of appendages. 
The female has a globular body 2 to 4 mm. long, which, 
bears two large egg-sacs. It is attached to its host, a poly- 
chaete worm, by means of a chitinous fixing organ, through 
this there protrudes into the worm a mass of vacuolated 
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