196 . report— 1878. 



thetically point to a six-legged transparent Nauplius as to the earliest 

 larval condition of Euphausia. This supposition has since been confirmed 

 by the examination of a considerable number of free-swimming Euphausia 

 larvae. Besides the larvse, which were in various stages of progress, I fished 

 up, he says, some ova from which I procured some Nauplii of the youngest 

 form, but as my observations on the embryonic development of the Schizo- 

 poda have not been concluded, I shall only describe the ovum containing 

 a mature larva." (PI. V., fig. 2.) 



" The ovum is a complete ball, in which one can distinguish two mem- 

 branes. Between the exterior membrane — the extraordinarily delicate 

 Morion — and the inner, the yolk skin, is a fluid clear as water, which 

 I have also seen in the ova of Penams. The yolk skin covers closely the 

 now quite mature and highly transparent larva, which latter shows three- 

 distinctly developed pairs of extremities. Through the movements of the 

 larva the egg-membranes are torn, and there escapes a peculiar animal, 

 on the oval body of which three pairs of appendages are attached which 

 exhibit the peculiarities of the Nauplius form of Crustacea." 



" The first pair is simple, while the two others are branched and articu- 

 lated into three joints, i.e. two basal and the terminal ; the only existing 

 opening is the oral aperture which is in the median line between the 

 base of the third pair of appendages. It appears in the form of a very 

 small hole which leads to a narrow oesophagus. With the exception of 

 red tint on the ventral surface, the larva is otherwise colourless and 

 transparent, and it is with much difficulty that some of the interior 

 organs can be distinguished." 



Herr Metschnikoff was able to trace some of the early changes, and was 

 in hopes to be able to remove some of the objections against Fritz-Miiller's 

 treatment of the development of Penaeus. He tried to follow the various 

 alterations in the same specimen, but failed to keep the animals alive 

 after a short period in his vessels. He was however here enabled to 

 trace the changes which conduct, he says, the larva "into that condition 

 which Claus has already described," but remarks that all the forms 

 examined by him lost with their moulting the indented or crenulated 

 margin of the carapace, which shows that he had to do with another 

 species than Euphausia Mulleri of Claus. He concludes with saying that 

 he " must draw attention to a phenomenon which is common to the 

 Nauplius stage of Euphausia and Penaeus, the contemporaneous formation 

 of the several pairs of appendages succeeding the larval and swimming 

 feet." " It is," he continues, "remai'kable that such a mode of formation is 

 not observed in any Entomostraca which have been developed through the 

 Nauplius metamorphosis. I have examined in this relation the Cirripedes 

 and Branchiopoda, and became convinced that in these Crustacea the 

 maxillaries are developed apart from the other appendages, as has been 

 shown by Claus to be the case in the Copepoda." 



Professor Claus has given the subject his attention, but his researches, 

 like those of Fritz-Muller, were carried on upon specimens taken in the 

 high sea, without any immediate clue to the parent from which they 

 derived their origin. 



It is certainly remarkable that so advanced an observer as Professor 

 Claus should have been content to have drawn his conclusions from such 

 incomplete and unsatisfactory data, particularly as he considers that an 

 imperfect appreciation of the development of the Crustacea has occasioned 

 in recent davs the supposition relative to the genetic relationship of 



