21 
of thinwalled, wing-like outgrowths ventrally to the margins of 
the shield; they reach from the level of the maxillipeds to the 
posterior end of the cephalothorax. 
II. The Hydroid. 
Seven specimens of the Hydroid have been found; 3 of these 
consist only of polypes, 4 carry besides sexual individuals. The 
polypes are all of one kind, functioning at the same time as 
hydranths and as blastotyles. They originate from a network of 
anastomosing tubes united by a thin membrane. The membrane 
and hydrorhizæ are without perisarc as well as the polypes. According 
to the size of the colony the membrane coats a greater or lesser 
part of the external portion of the Sarcotretes scopeli, described 
above. As the latter always turns the ventral face, on which the 
Hydroid is attached, towards the fish, a shelter is provided for the 
Hydroid. Larger colonies cover the whole ventral face of the para- 
Site and embrace more or less also of its sides, but leave most 
of the dorsal face free; only round the base of the stalk the mem- 
brane may close as a ring. Generally only adult, egg-bearing 
Parasites carry the Hydroid; but in a single case a Sarcotretes, 
which had evidently not yet formed egg-strings, was found provided 
with a Hydroid-colony (Pl. I, Fig. 6). The youngest Hydroid found 
had only a single, and still undeveloped polype, in which no mouth 
Was perceptible (Pl. I, Fig. 4); another young colony contains 1 
large and 4 smaller polypes (Pl. I, Fig. 5); a third has several 
Polypes and coats most of the ventral face of its Copepod. In two 
Colonies a single or a few polypes bear medusæ-buds; and in the 
remaining two most of the fully developed polypes carry at their 
base a number of buds in various stages of development, some of 
them quite medusiform, showing two tentacles. Most richly pro- 
vided appears the specimen figured Pl. I, Figs. 1—3; the medusæ 
åre here so numerous and prominent that they are the first to 
attract attention and determine the aspect of the whole colony. 
