The South Australian Naturalist 
99 
A REMARKABLE CRUSTACEAN. 
Herbert M. Hale, South Australian Museum. 
During the dredging trip on February 2nd a quantity of 
'Small forms of Crustacea came up in the dredge. Amongst 
these were some examples of Gnathia, an Isopod not hitherto 
recorded from our State. The members of this genus rarely 
exceed 8 mm. in length. Tliey have a fascinating life 'history 
and are remarkable for an extraordinai\y dimorphism betweeji 
the sexes. The tiny early larva of the animal is ])arasitic in 
habit and obtains its meals from fishes, to which it fastens 
itself until satisfied. After a time the larva becomes very 
swollen, the gut being filled with, and greatly distended by, the 
juices sucked from the fish. After leaving its host for the last 
time, the larva moidts and continues the life CA^cle as adult male 
or female, in which stage it never feeds again, subsisting solely 
upon the stored food in the gut. While the larvae are much 
alike the adults present remarkable sexual differences. The 
female somewhat resembles the larva, but becomes still more 
swollen; the stored nourishment is absorbed by the ovary and 
all the other organs degenerate to make room for a mass of 
large eggs which occupy the whole body cavity. The female 
then, becomes merely a living egg-sac from which the young 
Gnathiae hatch out. The male, however, assumes an astonish- 
ing form. The head is large and massive, and furnished with a 
pair of grasping mandibles, the use of which is not definitely 
known; the head of the female is small. The body is segmented, 
comparatively narrow, and of quite different appearance from 
that of the female. In the male, the food ingested during larval 
life is assimilated and stored in the large liver. 
EVENING LECTURES. 
Photo. Evening, November 20, 1923. 
Mr. Horswill showed a large number of original photo- 
graphs of Tasmanian scenery, including fine pictures of snow 
scenes on Mount Wellington. Other members also exhibited a 
number of interesting pictures of natural history subjects. 
The exhibitors included Messrs. Thomas, Wallis, Ham, and 
Ising, Mrs Pearce, and Misses Correll.and I. Roberts. 
