APPENDIX, © 391 
fectly simple, straight intestinal canal is visible, possessing a 
mouth in front, and an anal orifice behind. In front, above the 
mouth, lies a simple, single eye. All the six forms of nauplius 
entirely agree in all these essential characteristics of organiza- 
tion, whereas the six fully developed forms of Crustacea belong- 
ing to them, Plate XI., are extremely different in organisation. 
The differences of the six nauplius forms are confined to quite 
subordinate and unessential relations in regard to size of body, 
and the formation of the covering of the skin. If they could 
be met with in this form in a sexually mature condition, no 
zoologist would hesitate to regard them as six different species 
of one genus. (Compare vol. i. p. 175.) 
Plate XI. represents those fully developed and sexually mature 
forms of Crustacea, as seen from the right side, which have 
ontogenetically (hence also phylogenetically) developed out 
of the six kinds of nauplius. Fig. A ¢ shows a freely swim- 
ming fresh-water crab (Limnetis brachyurus) from the order of 
the Leaf-foot Crabs (Phyllopoda), slightly enlarged. Of all the 
still living Crustacea, this order, which belongs to the legion of 
Gill-foot Crabs (Branchiopoda), stands nearest to the original, 
common primary form of nauplius. The Limnetis is enclosed in 
a bivalved shell, like a mussel. Our drawing (which is copied 
from Grube) represents the body of a female animal lying in the 
left shell; the right half of the shell has been removed. In 
front, behind the eye, we see the two feelers (antenne), and 
‘behind them the twelve leaf-shaped feet of the right side of the 
body, behind on the back (under the shell), the eggs. Above, in 
front, the animal is fixed to the shell. 
Fig. B ¢ represents a common, freely swimming fresh-water 
erab (Cyclops quadricornis) from the order of Oar-legged crabs 
(Eucopepoda), highly magnified. In front, below the eye, we 
see the two feelers of the right side, the foremost of which is 
longer than the hinder one. Behind these are the gills, and 
then the four paddling legs of the right side. Behind these are 
the two large egg-sacks, kei in this case, are attached to li 
cud of the hinder part of the body. 
