Il. GENERAL REPRESENTATION OF THE FAMILY. 
le order to facilitate the use of this large section it is divided into three chapters, the 
first of which contains a general view of the structure and development of the animals, 
the second of their habitation, biology and distribution, the third some general observations 
about the classification. Each of these chapters contains several sub-divisions. 
A. Structure and Development. 
a. The Female. 
This sex is known in all species. The body is nearly always a little flattened — 
seldom more than a little; if seen from below or from above it is ovate or globular. The 
young specimens are generally much longer than they are broad; the adults are now a little 
longer than they are broad, now the reverse; sometimes their broadest dimension is a little 
in front of, sometimes a little behind the middle. Specimens which are going to lay, or 
have commenced laying eggs, are always somewhat — probably as a rule much — larger 
than old ones which are emptied of eggs (pl. 6, fig. 3a shows such a female which is going 
to lay eggs, fig. 3c a female (with a male) which is emptied of eggs, both enlarged to 
the same scale). In consequence of this evacuation the animals frequently shrink and 
become vaguer of outline. We often happen to see specimens which have become crooked 
and irregular from pressure, otherwise all the animals are naturally symmetrical. The 
size of the adults varies considerably; in most species the diameter of the animal seen 
from below is */s—1'/2mm.; it can even decrease to about ‘3mm. (Homocoscelis mediter- 
ranea), and Choniostoma Hansenii G. and B. can obtain a lenght of 53 and a breadth 
of 55mm. As a rule there is a certain proportion between the size of the parasite and 
that of its host; however, it must be borne in mind that the parasites themselves differ 
in size according to their habitation in the marsupium or under the carapace; in the latter 
place they are comparatively smaller. As a matter of course, small Amphipoda cannot 
