BIGELOW: EARLY DEVELOPMENT OF LEPAS. bol 
others render doubtful the early differentiation of a genital cell in 
Moina; but Hicker (92, ’97) has contributed some important cyto- 
logical evidence favorable to Grobben’s conclusions. 
To summarize the comparison of Lepas with the Copepoda and Phyl- 
lopoda, it has been pointed out that — 
1. In Lepas, in Moina (Grobben), in Cyclops (Urbanowicz), and 
probably in the parasitic copepod Lernza (Pedaschenko) mesoblast 
originates from ectoblastic cells of the blastoderm around the blasto- 
pore. In Cetochilus (Grobben) and in Cyclops (Hicker) there is a 
disagreement with Lepas, in that the entoblast cells are said to originate 
from cells whose origin and position is similar to those which in the 
above mentioned forms produce mesoblast. 
2. In Lepas, Cyclops (Urbanowicz) and Lernza a single entoblast 
cell, in Cetochilus (Grobben) the “central entoblast” cell, at first lies 
in the blastopore and it, or its derivatives, are overgrown by the 
blastoderm. ie 
3. In Lepas, Cyclops (Urbanowicz), Cetochilus (Grobben) and 
Lernea (1?) (Pedaschenko) some mesoblast originates directly from 
the entoblast cell which lies in the blastopore, that is to say, the 
yolk-macromere is mes-entoblastic. In all of these except Cetochilus 
(Grobben) mesoblast also originates from ectoblastic cells around the 
blastopore. 
The foregoing comparisons of the germ-layer formation in Lepas and 
other Entomostraca in which early differentiation takes place, brings 
out many points of resemblance. But in some cases there are differ- 
ences apparently irreconcilable. One can scarcely believe that such 
contradictory statements as have been summarized in the preceding 
paragraphs are based upon observations all equally reliable. Renewed 
investigation of the uncertain points is much needed. The numerous 
resemblances even from the beginning of development, make it very 
desirable that the cell-lineage should in these cases be carefully studied 
so as to give a basis for accurate comparisons. Until such data are 
accessible it is unsafe to draw conclusions respecting homologies of cells 
or even of the germ-layers, 
In many Crustacea there is at the blastopore an immigration of 
many cells into the cleavage cavity, In some of these cases the cavity 
is up to that time filled with yolk. The cell-mass thus formed by 
immigration into the cleavage cavity is mes-entoblastic, and the meso- 
blast and entoblast are at first indistinguishable, or at any rate inves- 
tigators have failed to find distinguishing marks. As examples of 
