RECENT ADVANCES IN SCIENCE 45 



Structure and Development of the Eggs of Crepidula " (ibid. 

 Feb. 191 7). By means of a centrifuge it is possible to separate 

 the egg into three zones — yolk, oil, and an intermediate zone 

 containing nucleus, centrosphere, and cytoplasm. He finally 

 concludes that " The differentiation of daughter cells does not 

 depend upon a differentiation of their centrosomes or nuclei, 

 for the spindles may be turned about without changing the 

 differentiations ; nor does it depend entirely upon the segre- 

 gation of the movable parts of the cytoplasm or of the yolk 

 in one cell or the other, for these segregations may be reversed 

 without changing the differentiations ; nor does it depend 

 entirely upon the position and direction of the mitotic figure 

 and the cleavage plane with reference to the egg-axes, for these 

 may be forcibly changed as in equatorial first or second cleavages 

 without changing the normal course of differentiation in those 

 cells after the force has ceased to act. These may be con- 

 tributory factors in the differentiation of cells, but the principal 

 factor is evidently to be found in the spongioplasm which always 

 tends to come back to its normal form if it is stretched or dis- 

 torted, and which probably differs in structure in different 

 parts of the egg and in different stages of development." 



Other papers include : " The Rhythmic Contractions in the 

 mantle of Lamellibranchs," by Redfield (ibid.). 



A minute species of Phoronis, P. ovalis, was described in 1856 

 by Strethill Wright, but since that day has been lost sight of, 

 and it has been suggested that the form was really an immature 

 condition of a larger species. Harmer, however, in " On 

 Phoronis ovalis Strethill Wright " (Quart. Jour. Micro. Sci. 

 vol. lxii. Feb. 191 7), has been able to announce its rediscovery 

 on the coast of Northumberland, and also to show that Wright 

 was justified in considering it as a species. Examples, still very 

 small, with mature gonads are described and a very good 

 account of the anatomy is here provided. 



The lice found on man have been dealt with fairly fully 

 in Parasitology for Feb. 191 7. Nuttall furnishes a very full 

 account of the structure and mechanism of " The Copulatory 

 Apparatus and the Process of Copulation in Pediculus humanus." 

 In " A Contribution to the Bionomics of Pediculus humanus 

 (Vestimenti) and Pediculus capitis, " by Bacot, we have an 

 account of the laying, hatching of eggs, moulting, and general 

 habits, accompanied by full tables. P. humanus is the larger 



