530 
J. S. KINGSLEY. 
Bateson on Balanoglossus, and especially the Hertwigs’ Coe- 
lomtheorie and Sedgwick’s essay on metameric segmentation, 
and the light they throw on the origin of the mesoblast, I 
think we are justified in reversing the course of reasoning and 
concluding that, on account of the origin of the mesoblast, the 
primitive groove is the homologue of the blastopore. 
The hypoblast has recently been recognised in the yolk, 
though in a rather vague and indefinite manner. Only one 
recent author (Ayres, ’84), so far as I am aware, has had other 
views. The indecision has doubtless been caused by the late 
appearance of the archenteric, or rather mesenteric lumen. 
To this we will recur again ; but now I call attention to the 
fact that at the stages of figs. 4 and 5 the yolk is broken up into 
true cells, each with its nucleus and cell wall. 1 have yet to 
see any “ free yolk-nuclei.” In describing the development 
of spiders Balfour (’80 h ) refers to and figures cells migrating 
from the yolk and taking part in the formation of the meso- 
blast, and says that the middle part of the dorsal mesoblast 
arises largely, if not wholly, in this manner. On the other 
hand Patten (’84), treating of the development of the Phry- 
ganids, reverses the operation, and claims a migration of meso- 
blast into the yolk. My observations do not allow me to 
decide which of the two is correct; indeed, I have seen but 
very slight indications of any migration, and those would, as I 
interpret them, tend to show that part of the mesoblast which 
forms the heart may arise in this manner. This view (a 
migration of yolk-cells into the mesoblast) does not conflict 
with the more recent ideas of the origin of the mesoblast in 
triploblastic animals nor with the nature of the yolk as above 
expressed, but merely shows that it is archenteric rather than 
strictly hypoblastic. Mr. Patten’s views are rather difficult to 
reconcile with what we know of the origin of the mesenteric 
tissues in other Arthropods. It would seem to me that he 
has misinterpreted his facts. 
Of the closure of the blastopore or neural groove I have 
nothing to say, as I have seen no eggs between figs. 4 and 5. 
Still, judging from the appearance of the two, I think the 
