52 
The first abdominal segment always dilates considerably from its base towards its 
end, and the free posterior angle has a powerful, often spiniform, seta, the length of which 
varies between being a little longer than the following segment (Stenothocheres, pl. 1, fig. 11) 
and being longer than the whole abdomen, and plumose in its distal half (Choniostoma, 
pl. XI, fig. le). Inside or outside this seta and close to it there is always another seta, 
which, as a rule, is much shorter, and only in Spher. microcephala (pl. VIII, fig. 21) is 
remarkably long, though somewhat shorter than the first one. The second segment is 
sometimes shorter, and in this case not unfrequently somewhat narrower, than the first one, 
e.g. in Choniostoma, sometimes quite as long, and always without sete. In Stenothocheres 
(pl. I, fig. 11) the third segment, together with the not separated caudal stylets, forms a large 
and broad, elongate segment, much larger than any of the preceding ones, and incised 
posteriorly in the median line. In all other species the third segment, together with the 
caudal stylets, is nearly always somewhat, and generally much, smaller than the second 
segment, and the stylets are sometimes not set off from the segment, but most frequently 
distinctly articulated on it as two short, almost cylindrical joints. Each stylet has always 
a very long and thick, sometimes plumose, seta, which in Stenothocheres egregius is only a 
little longer than the abdomen, in Mysidion and Aspidoecia somewhat longer, though not 
nearly half as long as the cephalothorax, in Homoeoscelis, Spheronella and Choniostoma 
longer than half the length of the cephalothorax, and sometimes attaining to three quarters 
the length of this part, e.g. in Spher. dispar (pl. LX, fig. 3k). Outside this long seta each 
stylet has in Stenothocheres four, in the other species two or three, comparatively short sete. 
Whereas there were great differences between the females among themselves and 
between the males among themselves in the different genera and species, we see from the 
detailed description given above, that all larva I know are surprisingly uniform, so much 
so, that I have been able to find rather insignificant generic characters only in Stenothocheres 
and Homoeoscelis, as distinct from the four other genera; at the same time the larve of 
Mysidion and Aspidoecia — whose females deviate much from those of the other genera 
with regard to receptaculum seminis, the position of the genital apertures and the hingement 
of the ovisacs — deviate less from various larvee of Spheronella, than these differ from 
each other. 
Il. Further Development of the Larve. The larve, after making their way out 
of the ovisac, — at least as a rule, swim out and seek a new host. I cannot deny the pos- 
sibility that one or a few of the larve may remain in the branchial cavity or in the 
marsupium of the mother’s host, though I doubt it very much. In a marsupium which 
was infested beforehand [ have repeatedly found one or several larvee, which were 
decidedly invaders. [ met with the greatest invasion in a specimen of Hippolyte Gaimardii, 
where in one of the branchial cavities I discovered a very young female of Choniostoma mirabile 
and certainly more than fifty larvae and pup hinged on the gill-fibres (s. the special 
description below). 
