872 The Crustacean Nebalia and its Fossil A/ties, [November, 



xvii, Fig. 6), or a more advanced stage, particularly that of Pseu- 

 domma roseum, as figured by Sars, 1 we shall find that many of the 

 differential characters which, in the adult, separate the Phyllo- 

 carida from the Decapoda, are to be found i die young. In 

 Mysis and allies at the same stage as Metschnikoff' s Fig. 18 of 

 Nebalia (our Plate xv, Fig. 4), the 2d antennae are simple instead 

 of being bifid as in Nebalia ; there are no maxillipedes, and the 

 maxillae are, as in the adult, immediately succeeded by the eight 

 pairs of thoracic feet; moreover, there are no abdominal feet in 

 Mysis or Pseudomma, while three pairs are present in the young 

 Nebalia. But with the exception of the lack of abdominal feet 

 in the Mysidae at this stage, it may be thought upon the whole, 

 as has already been stated by Balfour, that " the development of 

 Nebalia is abbreviated, but from Metschnikoff's figures may be 

 seen to resemble closely that of Mysis. * * * There is in 

 the egg a nauplius stage with three [pairs of] appendages, and 

 subsequently a stage with the zoea appendages." It seems to us 

 that the comparison 2 here made is, as regards any resemblance to 

 a zoea, loose and inexact, whether applied to the Mysidae or to 

 the Phyllocarida. The stage of the Mysidae succeeding the 

 nauplius is characterized by the presence of the rudiments of 

 eight pairs of appendages, the two pairs of maxillae, and the six 

 pairs of thoracic feet of the Schizopodous type, while the zoea 

 has no thoracic feet at all, so that it would appear that the Schiz- 

 opods do not pass through a genuine zoea state like that of the 

 higher Decapods. Nor on the other hand is the Nebalia stage 

 represented by Metschnikoff's Fig. 18 (our Fig. 4) a zoea stage, 

 for the embryo has the rudiments of eight pairs of thoracic feet, 

 and besides those of three pairs of abdominal feet, while there is 

 a well-marked carapace and rostrum, as well as procephalic lobes 

 with eyes, all these parts not being developed in the embryo 

 Mysidae. 



But whatever may be said of the resemblances between Nebalia 

 and the Mysidae at an early period after the nauplius stage has 

 been discarded, when we compare the later stage represented by 

 Metschnikoff's Fig. 19 (our Fig. 5, Plate xv) with the latest larval 

 stage of Pseudomma (see Sars's Fig. 23, our Plate xv, Fig. 6), 



1 G. O. Sars, Monog. over Mysider, Heft. I, Taf. IV, Fig. 23. 



3 Claus (Genealog. Gundlage des Crust. Systems, p. 31), as we find since writing 

 the above, does not accept Metschnik t>ff*j omp imm of the young Nebalia with 

 the zoea, although he does not give the reasons for bis dissent. 



