154 
ETCllAnn ASSIIETON. 
that there would then be a very striking difference compared 
with other vertebrates. In all other vertebrates the blasto- 
pore lip is the growing point for growth in length, and 
growth in length begins at once, therefore showing itself 
clearly in the origin of denterogenetic (peristomial) mesoderm 
from the angle of the lip laterally, notochord dorsally, and 
denterogenetic epiblast superficially. This condition is well 
known not to occur until some hours later — in the chick about 
the twelfth to fifteenth hour of incubation. So we should 
have to account for a very remarkable disappearance and 
reappearance of this proliferating centre. 
Again, Patterson in his second series of experiments says 
that an injury made during the involution process is found 
in the entoderm, posterior to the position of the nineteeth 
pair of mesoblastic somites. We are faced with the 
following dilemma. We can Irardly have a proliferating 
blastopore lip formed as in other vertebrates so long as the 
outer layer is turning in to form entoderm. Therefore this 
proliferating lip must come into being after the cessation of 
that pi-ocess. Any injm-ies made to the involuting membrane 
must surely occur in front of, or beyond, all the tissues, 
mesoderm included, which are produced by the proliferating 
lip when it comes into being. 
But fig. 50 shows such an alleged injury far posterior to the 
nineteenth pair of somites. The injury ought to be in front of 
all the primitive streak mesoblast, whereas, according to the 
figure, thei’e are many somites of mesoblast in front of the 
injury. 
Another argument which is difficult to follow is the sugges- 
tion on p. 99 that certain “cavities in the dorsal lip” 
ai-e the homologues of Kupffer’s vesicle. It is surely well 
enough established that whatever the physiological meaning 
may be of Kupffer’s vesicle in Teleostean development, it is, 
as a cavity, part of the gut-cavity. According to Patterson 
the archenteron is the cavity roofed in by the inturning edge 
of the blastoderm. Yet here he says that these vacuoles above 
this roof are homologous to the Kupffer vesicles, which are 
