442 GEOLOGICAL SURVEY OF THE TERRITORIES. 
parison. The early stages of Mysis, as worked out by Van Beneden 
and Claparéde, and of Nebalia, aremuch alike; the formation of the blasto- 
derm is much the same. The nauplius stage in the egg is nearly iden- 
tical in both, but beyond this the parallelism ceases to be an exact one; 
Nebalia turns off and follows quite a different developmental path from 
Mysis or any Decapod. If we compare the young of Nebalia, taken from 
the brood-sac, with that of Mysis, as figured by Claparede (Plate XVII, 
abf. ant” ant 
Fig. 68.—Embryo of Nebalia ready to hatch, enlarged; ant’, Ist antenne; ant’, 2d antenne; ab.f., 
abdoniinal feet or uropoda. The first maxilla crosses the thoracic feet. After Metschnikoff. 
fig. 6), or a more advanced stage, particularly that of Pseudomma roseum, 
as figured by Sars,! we shall find that many of the differential char- 
acters which, in the adult, separate the Phyllocarida from the Decapoda, 
are to be found in the young. In Mysis and allies at the same stage as 
Metschnikoff’s, fig. 18 of Nebalia, (our Plate XX XIII, fig. 4,) the 2d 
antenne are simple instead of being bifid as in Nebalia; there are no 
maxillipedes, and the maxilla are, as in the adult, immediately suc- 
ceeded by the eight pairs of thoracic feet; moreover there are no ab- 
dominal 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 Myside@ 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. . . . Thereis in the egg a nauplus stage 
with three [pairs of] appendages, and subsequently a stage with the 
zoéa appendages.” It seems to us that the comparison? here made is, 
‘as regards any resemblance to a zoéa, loose and inexact, whether ap- 
plied to the Myside or to the Phyllocarida. The stage of the Myside 
succeeding the nauplius is characterized by the presence of the rudi- 
ments of eight pairs of appendages, the two pairs of maxillz, and the 
six pairs of thoracic feet of the Schizopodous type, while the zoéa has 
no thoracic feet at all, so that it would appear that the Schizopods do 
not pass through a genuine zoéa state like that of the higher Decapods. 
Nor on the other hand is the Nebalia stage represented by Metschni- 
koft’s fig. 18 (our fig. 4), a zoéa stage, for the embryo has the rudiments 
of eight pairs of thoracic feet, and besides those of three pairs of ab- 
dominal feet, while there is a well-marked carapace and rostrum, as well 
1G. O. Sars, Monog. over Mysider, Heft 1, Taf. IV, fig. 23. 
?Claus (Genealog. Gundlage des Crust. Systems, p. 31), as we find since writing 
the above, does not accept Metschnikott’s comparison of the young Nebalia with the 
zoéa, although he does not give the reasons for his dissent. 
