Dr. F. Miiller on the Metamorphoses of the Prnmt. 109 



that section of the body which is amalgamated with the carapace ; 

 with the progressive extension of the carapace the heart hkewise 

 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 larva; of Decapods. It resembles 

 the foremost dilated section of the younger Stomapod lan'ae 

 recently described by me. The intercrossing trabecule of the 

 interior are wanting, and there are only two iissures 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 

 trabeculse, 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 reneU aeem 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 Zoete. 



The above are the parts which remain nearly unaltered during 

 the whole of this ))eriod. 



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 bcconie 

 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 



