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scribes, first dividing to form four basal cells (corresponding in origin 

 and position with the four basal entomeres of annelids and mollusks) 

 and four much larger upper cells which correspond to the fourth quartet 

 of micromeres in annelids and mollusks. The posterior of these cells 

 always divides before the others, sometimes equally and symmetrically 

 as in Discocoelis (Lang), but more often unequally. The cells thus 

 formed give rise to a part of the archenteron and not, so far as can 

 be determined, to mesoblast. 



These observations show that the mesoblast of polyclades is of 

 ectoblastic origin; and they suggest that the origin of mesenchyme-cells 

 from the second (U n i o , r e p i d u 1 a) or third (Physa, Planorbis) 

 quartets in gasteropods may be a vestige or ancestral reminiscence of 

 the mesoblast formation in the polyclades. They suggest further that 

 the mesoblast-bands (entomesoblast) of annelids and mollusks may have 

 been historically of later origin than the mesenchyme (ectomeso blast) 

 — a view which harmonizes, broadly speaking, with that of Meyer — 

 and that the two symmetrical entoblast-cells, into which the posterior 

 member of the fourth quartet divides in the polyclade may represent 

 the prototypes of the entomesoblasts of the annelids and gasteropods, 

 (E. B. W.) 



Mr. Cbampton briefly reviewed his observations on the early history 

 of the egg in Molgula manhattensis, as follows: 



The author emphasized the fact that development begins not with 

 the cleavage or fertilization processes, but even before. From the origin 

 of the primary oocyte until the final assumption of the adult form, 

 there is a continuous series of developmental changes, each stage being 

 based upon the preceding one and conditioned by it. 



The growth of the primary oocyte and the formation of the yolk 

 were considered at some length. A true "yolk-nucleus" arises, as the 

 author believes, from the nucleus ; and this by continued growth, and 

 later by fragmentation, gives rise to veiy small spherules which later, 

 by enlarging, form the yolk-spherules. The yolk-nucleus is an albumin- 

 ous body closely allied to, if not identical with, the yolk or deutoplasm. 

 This was indicated by a large number of microchemical tests. The 

 yolk-nucleus at a very early stage of the egg was also shown to be 

 the only albuminous body in the cell ; for the rest of the extra-nuclear 

 part of the cell is almost exclusively composed of pseudo-nucleinic sub- 

 stances. Evidence was cited which indicated that the yolk-nucleus was 

 formed by the nucleus, and that it enlarged by constant additions to 

 it from the nucleus. 



The more important results of a study of the maturation and 

 fertilization processes might be briefly stated, although a fuller account 

 will appear in the published paper. The first maturation spindle arises 

 entirely from the germinal vesicle. It is peculiar in that it is barrel- 

 shaped and does not, as far as can be determined, bear at either end 

 centrosomes or asters. The first polar body receives sixteen chromo- 

 somes, while sixteen remain in the egg. The second maturation spindle 

 is also barrel-shaped, and is also devoid of centrosomes and asters. 

 Eight chromosomes remain in the egg. The sperm entrance was de- 



