III. GENERAL REPRESENTATION OF THE FAMILY. 



In 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 knowu in all species. The body is nearly always a little flattened — 

 seldom more than a little; if seen from beloAV 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 aie 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 (pi. 6, fig. 3a shows such a female wliich is going 

 to lay eggs, fig. 3c a female (with a male) wliich is emptied of eggs, both enlarged to 

 the same scale). In consequence of this evacuation the animals frequently shrink and 

 become vaguei' of outline. We often happen to see specimens wliich 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 — IV2 mm. ; it can even decrease to about -3 mm. (Homoeoscelis mediter- 

 ranea), and Choniosfonia Hansenn G. and B. can obtain a lenglit of 5'3 and a breadth 

 of 5-5 mm. 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 diff'er 

 in size according to their habitation in the marsupium or under the carapace; in the latter 

 place they are compai-atively smaller. As a matter of course, small Ampliipoda cannot 



