IS() The America It (ieoJotjhf. Scptomher, ih95 
very ])f)sitive evidence, amouutiiig virtually to certainty, that 
the protaspis had tive pairs of limhs attaclied to the cephalic 
portion, behind \vhicl\ was an alxloniinal portion containing 
the forjnative elements out of which all the posterior somites 
and appendages were developed. 
VII. Thk Ckustacean Nauplius. 
The name Xanph'ns was first used by O. F. Miiller--' to desig- 
nate a minute crustacean believed to represent an adult animal. 
Afterwards it was found to be a larval stage of Ci/rh)p.s\ but 
because it agreed in structure with the larviv of many other 
Crustacea the name was retained for that type of larval form 
and is now in general use. Primarily it is supposed to repre- 
sent the first free-swimming stage after the escape of the ani- 
mal from the egg. Hf>wever, many species are quite fully devel- 
oped when leaving the egg, and undergo comparatively slight 
subsequent nietan orphoses, and in these and other species 
there may be developed in the egg an embryo having some of 
the characters of the nauplius. Therefore, the term is also 
applied to all cases where a certain assemblage of nau})lian 
characters occurs in the development of any crustacean. IMius 
it may be considered as a stage of develo])ment not restricted 
to a definite period of ontogeny. 
The adult Apiis possesses so many uauplian features, and in 
its development passes through such simple metamorphoses, 
that it has been aptly considered by Bernardi^ as a nauplius 
grow^n to maturity. Balfour^ also states that the chief point of 
interest in the development of . -I y>/^s• "is the fact of the pi'imi- 
tive Nauplius form becoming gradually converted without any 
special metamorphoses into the adult condition."* This form, 
together with the nauplii of other crustaceans and the study of 
the larval and adult characters of the trilobites, ought to af- 
ford definite knowledge of the characters possessed by the an- 
cestral forms of the Crusatcea. 
Before farther examining the nauplius it may be well to state 
the characters, which, on the grounds of comparative anatomy 
and pliylogeny, are believed to represent the ])riniitive adult 
crustacean. It will be seen that, in many respects, the trilobite 
*The adult Apun properly has five pairs of cephalic limbs. A sixth 
pair of appendao:es has been correlated as maxillipedes. though from 
their innervation they seem to i)e luetastoinie and honioloiious with the 
chiiuria of Liiiniliis. 
