THE GENUS PTERYGOTUS 199 
is no more than might be expected, when we take into consideration 
how common a thing it is, for some form of a group to retain more 
or fewer of the characters usually found only in the young of that 
group; and perhaps the only subject for astonishment is that adult 
Copepoda, with still fewer limbs, have not yet been discovered. A 
Copepod just hatched is, in fact, a very different creature from the 
adult, as has been known since the observations of Jurine upon 
Cyclops. 
Rathke, who has devoted particular attention to the development 
of the embryo in this genus, maintains that of the three pairs of 
locomotive appendages, with which alone the young is endowed 
when it leaves the egg, the two anterior eventually become the 
antennules and antenne, while the posterior are neither the man- 
dibles nor the first pair of manilla, but the rudiment of the ‘ mains ” 
of Jurine. The young Cyclops is in addition provided with a large 
epistomo-labral plate. Its further changes consist chiefly in the 
elongation of the body, and the gradual and successive acquisition of 
the thoracic members. 
The resemblances of Prerygotus to the Dzastylide do not extend 
to the most important and characteristic features of its organisation, 
and even were we to combine together into one form all the 
analogous peculiarities which have been noted in these, in Stomapoda, 
in Schizopoda, and in larval Podophthalmza, we should not get a 
sufficiently near approximation to Péerygotus to justify the arrange- 
ment of the extinct genus in either of the orders of the higher 
Crustacea. As 1 hinted above, however, a stronger case might be 
made out for the Copepoda. Combine the body of Safpherina with 
the eyes and antenne of Coryceus, the mandibles and maxille 
of Calanus, the epistoma and metastoma of Pontella, and the total 
number of appendages of a copepod larva, and something marvel- 
lously like a Pterygotus would be produced. But such an animal 
would not be a Pterygotus, and even if it were, it would differ so 
widely from any of the known Cofepoda, that its association 
with the members of that order would be a step of very question- 
able propriety. Confining the argument to known and existing 
Copepoda, the differences between them and Pterygotus are sufficiently 
striking. 
No Copepod has truly chelate antenni or antennules, and none 
present any approximation to the remarkable teeth with which the 
chele of Prerygotus are beset. All known Copepods have large 
thoracic appendages ; no trace of such organs has yet been discovered 
in Plerygotus. 
