92 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
the blastoderm, contains only ectoblastic material. An exception is to 
be noted in the case of Nussbaum, who saw the mesoblast apparently 
proliferating from the edge of the blastoderm. The cell ad? according 
to his interpretation, then, contains all the ectoblast and the mesoblast. 
The erroneous interpretations of the earlier observers are largely 
explained by the fact that their observations were almost exclusively 
confined to living eggs, in which the nuclear conditions are hidden. 
Without sections or transparent preparations divisions of the yolk-cell 
might be easily overlooked. Lang (78) and Nassonow (’87) figured for 
Balanus, and Nussbaum (’90) for Pollicipes, distinct protoplasmic radi- 
ations in the yolk-cell, but failed .to see their significance as indicating 
division. Iam convinced that the structures seen were asters or archo- 
plasmic radiations. Korschelt und Heider (90) made the suggestion, 
based on Nassonow’s figures, that the yolk-cell ed? divides and contributes 
cells to the blastoderm. 
Groom (’94) described the yolk-cell cd? in the case of all cirripedes 
whose development he observed, as a macromere giving rise in succession 
to a number of “ blastomeres,” which are added to the blastoderm. He 
proved conclusively that the “ protoplasmic” cell ab? (his “first blasto- 
mere,”’ my “first micromere ”) does not give rise to all of the ectoblast, 
as supposed by all previous observers. According to his account several 
cells (estimated at nine or ten) are cut off from the yolk-cell after the 
first cleavage, and with the derivatives of the “ first blastomere ” form 
the blastoderm. 
Several years ago, without knowledge of Groom’s results, owing to the 
inaccessibility of the literature, I (’96) found that in Lepas fascicularis 
the yolk-macromere divides several times, practically synchronously with 
the divisions of the other cells, thus contributing to the formation of 
stages of 2, 4, 8,16 and 32 cells. This confirmed Groom’s results in 
general; but as to the order, method, and number of the divisions I was 
forced to dissent from his account. 
According to Groom’s description there is great variation in the num- 
ber, order, and position of cleavages both in the yolk-cell and in the 
other cells of the cleaving egg. He concluded that the cleavage of the 
cirripede egg is decidedly irregular. He writes (p. 140), “there is no 
constancy in the mode of growth of the blastoderm over the yolk ;” and 
mentions (pp. 139-140) many of the variations which occur. 
Many of these supposed variations are certainly misinterpretations 
due to errors in orientation, and others are apparently based upon ab- 
normal eggs. Mention may be made of several cases. Groom states 
