418 GEOLOGICAL SURVEY OF THE TERRITORIES. 
Hence the three orders of Branchiopoda, the Phyllocarida, and the Dee- 
apoda (with the Tetradecapoda) must, it appears to us, have indepen- 
dently of each other originated from some Laurentian Nauplius-like 
form. 
The views of Claus and some important criticisms upon them are 
given at length by Mr. Balfour in his valuable Comparative Embryol- 
ogy, while we would observe that neither Claus, Dohrn, nor Balfour 
appear to refer to the paleontological history of the Crustacea. 
Professor Claus, in his suggestive work on the genealogy of Crustacea, 
according to Balfour, claims that the later Nauplius stages of the dif- 
ferent Hntomostracan groups and the Malacostraca (Peneus larva) ex- 
hibit undoubted Phylopod affinities. He therefore postulates the earlier 
existence of a Protophyllopod form, from which he believes all the Crus- 
tacean groups to have diverged. This ancestral form, Balfour thinks, 
had three anterior pairs of appendages similar to those of existing 
Nauplii. It may have had a segmented body behind the third pair of 
appendages provided with simple biramous appendages. <A heart and 
cephalothoracic shield may also have been present, though the existence 
of the latter is perhaps doubtful. There was no doubt a median simple 
eye, but, adds Balfour, it is difficult to decide whether or no paired com- 
pound eyes were also present. The tail ended in a fork, between the 
prongs of which the anus opened, and the mouth was protected by a 
large upper lip. ‘In fact, it may very probably turn out that the most 
primitive Crustacea more resembled an Apus larva at the moult imme- 
diately before the appendages lose their Nauplius characters (fig. 208 
B), or a Cyclops larva just before the Cyclops stage (fig. 229), than the 
earliest Nauplius of either of these forms” (Balfour, p. 418). 
That the Decapods and Phyllopods may have originated from such a 
form as Balfour thus depicts seems to us to be quite probable. 
Mr. Balfour, on page 380, states that “the Branchiopoda, comprising 
under that term the Phyllopoda and Cladocera, contain the Crustacea with 
the maximum number of segments and the least differentiation of the 
separate appendages. This and other considerations render it probable 
that they are to be regarded as the most central group of the Crusta- 
ceans, and as in many respects least modified from the ancestral type 
from which all the groups have originated.” 
Against this view may be, however, offered two criticisms. The ex- 
cessive number of segments in the Apodida@ is paralleled among the 
Tracheata by the Chilopods, in which the numerous segments appear to 
have each two pairs of feet, and these Myriopoda are probably not the 
more ancestral, generalized Myriopodous forms, the Pauropus and 
Kurypauropus being much more so, these forms having few segments, 
each with no more than one pair of feet. The excessive number of seg- 
ments in Apus and the irrelative repetition of abdominal feet appear to 
us to be signs of a vegetative repetition of parts in a type which has 
culminated, and is subject to decline and extinction. 
Again, i in Poli yartemia, with its 19 pair of feet, where Artemia has the 
normal number of eleven (within its family limits) appears to us like 
Apus to be a highly specialized and extreme form; Artemia being the 
more generalized, though, as compared with Br anchipus, a degrada- 
tional form. 
The view that the Phyllopods “are members of a group which was 
previously much larger and the most central of all the Crustacean 
groups,” is not fully sustained by zodgeography or paleontology. At 
present all Phyllopods are fresh-water forms, and they are exceptionally 
rare TORUS, occurring only locally, though every continent has its quota 
