A STUDY IK MORPHOLOGY. 
63 
and show the embryos in dorsal view, as seen under a very low magnifying power, 
but they are so much like Fritz Muller’s figures, that we must acknowledge that 
the credit of the first discovery of a Malacostracan Nauplius belongs to Dana, and 
that up to the present time this is the only case in which a Nau'plius has been traced 
to an egg which could be definitely identified as that of a specific adult Mala¬ 
costracan, although his account is so imperfect that in itself it is certainly not 
sufficient to prove the existence of the Nau'plius stage at all. 
In 1861 Fritz Muller found, at Desterro. in Brazil, a single specimen of a Naup- 
lius (“Die Yerwandlung der Garneelen.” Erster Beitrag von Fritz Muller, in 
Desterro, Arch. f. Naturgeschichte, 1863, p. 9), which he traced, through other speci¬ 
mens which were also collected in the ocean, to a form which he believed to change 
into the youngest Zoea of a species of Penoeus. The series of stages is so satisfactory 
that there is no reason for doubting the accuracy of his conclusion, but the chances 
for error, in the attempt to trace Crustacean development from isolated specimens, are 
so very great that the statement has not received unqualified acceptance. 
The only other recorded observation of a Malacostracan Nauplius is not among the 
Decapods, but in the more embryonic Schizopods. These observations, which were 
made by Metschnickoff, would tend to corroborate those by Muller, but they are 
unfortunately open to the same criticism. He did not actually rear the larvse and 
trace them to a specific adult, and although there would in ordinary cases be no doubt 
of the correctness of his conclusion, a careful analysis of his papers will show that 
there certainly is a possibility of error. 
In the spring of 1868 he collected from the surface of the ocean at Messina a few 
early stages in the development of a Crustacean, which he believed to be Euphausia 
mulleri (Claus), and showed (“ Ueber ein Larvenstadium von Euphausia ” von 
El. Metschnickoff in Petersburg, Zeit. £ Wiss. Zool., xxix., 1869, p. 479, taf. xxxvi.) 
that it passes through a well-marked Nauplius stage, of which he gives three figures. 
The following year, at Villafranca, he collected a good supply of young larvee and 
floating eggs in advanced stages of development, and was thus enabled to supplement 
his first paper by a second (“ Ueber die Naupliuszustande von Euphausia ,” von Elias 
Metschnickoff, Zeit. f. Wiss. Zool., xxi., 1870, p. 380, taf. xxxiv.) m which he gives a 
minute account of the Nauplius from the time it leaves the egg until it changes into a 
form somewhat similar to the youngest stage of Euphausia , which had been previously 
described by Claus (“Ueber einige Schizopoden und niedere Malacostraken Messinas,” 
von Prof. Dr. C. Claus, Zeit. f. Wiss. Zool., xiii., 1863, p. 422). Claus had supposed 
this to be the stage in which the larva leaves the egg, and he says (p. 450), “ Diese 
Larve bin ichgeneigt fur die jiingste aller freieren Entwickelungsformen der Euphausia 
anzusehen.” He subsequently learned, however (“ Untersuchungen zur Erforschung 
der Genealogischen Grundlage des Crustacean-Systems,” p. 9), that he had been in error, 
since he afterwards found, in an Atlantic and also in a Mediterranean species, an earlier 
Protozoea stage, which changed into the Zoea described in his first paper. It therefore 
