ARTHROPODA 277 
pedia are hermaphrodite, there are certain genera, e.g. Zb/a and 
Scalpellum, in which males have been described. These are 
dwarfed forms, often very degenerate, which live usually two or 
three at a time within the mantle of the normal hermaphro- 
dite or female, and are known as complemental males. 
Their degree of degeneracy varies within wide limits, and it 
seems as a rule to increase with the depth of the water in 
which they live. Three species of Scalpellum which inhabit 
shallow water, S. peronii, S. rostratum, and S. villoswm, are pro- 
vided with males which have retained the division of the body 
into a capitulum and a peduncle; in eight other species, which 
extend to a depth of 700 fathoms, the males have lost this 
division of the body, but still retain rudiments of shell 
valves; in thirteen other species, which were almost all taken 
from depths of upwards of 1000 fathoms, even these have dis- 
appeared. The male of Scalpellum regiwm, one of the most 
degenerate, is a minute animal about 2 mm. long, attached to the 
inner surface of the scutum of the female by means of minute 
antennae which are provided with cement glands. No other 
appendages are visible. The body is oval, rounded at each 
end, and covered with a chitinous cuticle, which is produced 
into short spines. The alimentary canal is rudimentary and 
functionless, the mouth does not open, and the mouth append- 
ages are gone. There are a supra-oesophageal ganglion, con- 
necting cords, and one infra-oesophageal ganglion ; the eyes 
have disappeared. The generative apparatus alone is well 
developed, but the female organs have completely disappeared, 
the testis and vesicula seminalis are single. 
The remarkable genus Scalpellum presents yet a further 
complication in its sexual arrangements. Its species may be 
arranged in three groups: 
A. Those which are truly hermaphrodite, and in which no 
complemental males exist. Ex. Scalpellum balanoides. 
B. Those which are hermaphrodite and yet possess comple- 
mental males. Ex. Scalpellum villosum, peronu, vulgare, 
rostratum, etc. 
C. Those which are unisexual, the females large and normal, the 
males minute and living parasitically in the mantle of 
the female. Ex. Scalpellum ornatum, regium, vitrewm, ete. 
