W142 Dr. F. Muller on the Metumorphoses of the Prawns. 
apical half, and beset with long bristles; this is almost con- 
stantly in a whirling motion. 
In the ¢ai/, the lateral plates are now moveably articulated 
upon a short basal joint and beset with long plumose set; the 
middle piece (the seventh abdomina] segment) appears to be 
longer and narrower, as though the two divergent branches had 
been pressed together to almost complete amalgamation; the 
‘sete of the Zoéa are retained in their full number, but coutracted 
into short spines. The anus is situated at the base of this last 
segment., 
About the same time a considerable alteration of the heart 
takes place ; it acquires four new fissures for the entrance of the 
blood, and internal muscular trabeculee. 
In this Mysis-like form our larva was observed from scarcely 
2 mill. to 4°5 mill. in length. During this period the auditory 
organs, the pincers, and ambulatory feet are developed, and the 
rudiments of the mandibular palpi, abdominal feet, and branchize 
make their appearance. 
The flagella of the antenne become elongated and divided 
into joints; in animals of 4 to 4°5 mill. in length the two flagella 
of the inner antenne are three-jointed ; the outer one, which is 
somewhat shorter, bears about seven bacilli; the flagellum of the 
outer antenna attains nearly the length of the scale. 
In the basal joint of the inner antenna the auditory apparatus 
is formed. The lower third of this jot becomes inflated ex- 
ternally, the swelled portion having a crescentiform anterior 
margin. In the interior of this inflation an elongated ‘cavity is 
soon observed (in animals of 3 mill. in length). A little later 
there appears in the cavity a globular, strongly refractive otolith, 
and in the crescent-shaped anterior emargination three or four 
short, plumose sete, bulbous at the base (fig.9). The otolith 
does not appear to lie freely in the cavity, but (as is the case in 
the tail of Mysis) to be supported by delicate filaments, which 
issue from a ganglion situated inwards from the cavity. 
The extended spine of the upper lip begins to disappear, but 
is still recognizable as a minute point in animals of 4°5 mill. in 
length. The palpi make their appearance on the mandibles, 
about the time of the formaticn of the otoliths, in the form of 
small mamille, which are soon elongated, but remain unjointed 
and destitute of sete. 
The pincers (chele) are indicated, even in animals of 2°8 mill. 
long, by the still unjointed inner branch of the corresponding 
three pairs of feet acquiring a small process on the inner margin 
a little below the apex. In animals of 3:5 mill. in length, these 
feet are already divided into joints as in the mature animal, and 
this process (the immoveable finger) attains two-thirds of the 
