82 H. J. HANSEN. 
two thirds of the genera the mouth-parts are similar in both 
sexes and in immature specimens, but in nearly one third of 
the genera the adult females have the basal half of the 
maxillipeds exceedingly expanded, being adapted for pro- 
ducing a current of water through the marsupium, while the 
distal part of the same appendages and all other mouth-parts 
are strongly reduced. One is apt to suppose that this meta- 
morphosis must be associated with one of the modifications 
of the incubatory chamber, but it is far from being so. Some 
instances may be enumerated. Vireia and Dynamene have 
a normal chamber formed only by the very large lamelle, but 
the mouth-parts are normal in the females of the former, 
exceedingly metamorphosed in those of the latter genus. 
Spheroma and Cymodoce have marsupial lamelle of the 
same size, but in the former genus the mouth-parts are normal, 
in the latter metamorphosed. The metamorphosis or non- 
metamorphosis of the mouth-parts is, on the contrary, con- 
nected with and even dependent on the shape of the end of 
abdomen, as will be shown in Chapters III and V. 
TI]. MetramorrHosis or MoutrH-Parts In FEMALES OF SEVERAL 
GENERA. 
In all genera the mouth-parts in adult males and immature 
specimens of both sexes of the same species are always com- 
pletely alike. In the sub-families Limnoriine and Plakar- 
thriinee and in the major part of the genera of the sub-family 
Sphzerominee the mouth-parts in females with brood are similar 
tothose in the males, but in some genera the mouth-parts insuch 
females are metamorphosed in a very peculiar way. In Lim- 
noria (Leach), Sphzroma (Bosc), Hxospheroma (Stebb.) 
Isocladus (Miers), Zuzara (Leach), Cymodocella 
(Pfeff.), Cassidinopsis (n. gen.), Paraspheroma (Stebb.), 
Vireia (Dollf.), Cassidinidea (n. gen.), Leptospheroma 
(Hilg.), Ancinella (n. gen.), and Plakarthrium (Chilt.), 
the mouth-parts of females carrying eggs or young are— 
according to my investigations—shaped as in immature speci- 
