Dr. F. Muller on the Metamorphoses of the Prawns. 109 
that section of the body which is amalgamated with the carapace ; 
with the progressive extension of the carapace the heart likewise 
moves its position further back. Thus, in the older Nauplius, it 
is situated above the third pair of feet (upper Jaws), but now 
over the sixth and seventh (footjaws). The structure of the 
heart, however, differs remarkably from that of the older ani- 
mals, and indeed of the other larve of Decapods. It resembles 
the foremost dilated section of the younger Stomapod larvee 
recently described by me. The intercrossing trabecule of the 
interior are wanting, and there are only two fissures for the en- 
trance of the blood, situated on the lower side of the posterior 
part of the heart. These two fissures are unusually striking ; 
and I think I may state with positive certainty that they are the 
only ones. I have frequently and for a long time traced the 
course of the blood-globules through the heart and in its vicinity, 
and never seen them enter anywhere but here: I have sometimes 
seen blood-corpuscles coming from the fore part of the body 
glide along close by the heart, in order to reach these posterior 
orifices. Moreover the other fissures, which are subsequently 
easily distinguishable notwithstanding the internal apparatus of 
trabeculz, could hardly now be overlooked in the simple sac. One 
vessel originates at the anterior extremity of the heart, and a 
second below its rounded posterior extremity. Valves were 
seen at the origin of the former. Other vessels seem to be 
wanting. A great part of the blood returning from the anterior 
part of the body takes a circuitous course through the carapace, 
as in other Zoée. 
The above are the parts which remain nearly unaltered during 
the whole of this period. 
Of the new parts which make their appearance, the paired 
eyes are to be regarded as the first in order of time; for their 
earliest traces were already recognizable in the oldest Nauplius. 
They form a mass of considerable size, lying above the anterior 
part of the carapace, and projecting beyond the frontal margin 
(fig. 3). Near their external posterior angle a black pigment- 
spot makes its appearance, from which radiating lines may soon 
be traced to the surface of the future true eye. Before and 
within this the thickened visual nerves may be distinguished, 
behind which there remains a free space, subsequently traversed 
by a muscle. The eyes, which are at first quite contiguous, now 
rapidly become separated, so that the central eye and the whole 
breadth of the ganglia between which it is situated again become 
visible from above. 
Peculiar structures, the signification of which I do not know, 
and which appear to be deficient in other species observed, are 
the two hemispherical transparent buttons which project from 
