EARLY ONTOGENETR! PHENOMENA IN MAMMALS. 271 
Chapter VI. 
Lastly, Hubrecht wishes to revise the classification of 
vertebrates in the light of this supposed homology of all 
outer trophic or protective layers within the phylum. 
He says (p. 81) : “And it then, of course, strikes us, sup- 
posing all these different outer covering layers during early 
larval life to be the remnants of an early larval envelope, of 
which we find no trace in Amphioxus, the cyclostomes, and 
the Elasmobranchs, that the deep significance hitherto 
attached to the foetal membranes as a means of sub-dividing- 
the Vertebrates into the primary groups of Amniota and 
Anamnia runs great risk of losing much of its significance.” 
So Hubrecht, leaving out of consideration the Hemi- 
chordata and Urochordata, divides the higher chordates into 
four “ super-classes,” namely Cephalochordata (for Amphi- 
oxus), Cyclostomata (for the Marsipobranchs), Chondrophora 
(for the Elasmobranchs), and Osteophora (for the Amphi- 
bians, Dipnoans, Ganoids, Teleosteans, Reptiles, Birds, and 
Mammals). 
Seeing that the bond of union for these last seven groups 
is the supposed presence of a larval envelope, one wonders 
that Hubrecht has not coined a word suitable to this pheno- 
menon instead of falling back upon the presence and absence 
of bone. Does the neglect suggest a lack of faith ? 
On p. 17 Hubi-echt writes: “A tendency to exchange the 
radial for a bilateral symmetry and to separate the coelom 
from the enteron must at one time have characterised certain 
coclenterate ancestral forms, as has already been advocated 
by Sedgwick (’84) and by myself (’05) on eai-lier occasions. 
It is not straining the imagination to assume that in this line 
of descent closely-related forms may have developed, some 
with, others without a larval envelope, temporarily ensheath- 
ing the cellular elements that will build up the embryo itself, 
and thus foreshadowing the separation among their later 
vertebrate descendants of such with and such othei-s without 
a trophoblast.” 
