584 BULLETIN OF THE 



process of cell division. But tlie second " amphiaster de rebut " arises directly 

 from the internal half of the first. One may compare the two polar globules 

 to a cell originally single. 



In the cases of superfecundation the union of two male asters to a female 

 pronucleus results in a conjugate nucleus, which soon gives place to a tetraster, 

 in which four equidistant stars occupy the corners of an imaginary square, the 

 sides of which are formed by the intranuclear filaments. In division each of 

 the four groups of filaments (spindles) shows a series of enlargements which 

 divide and migrate as usual. The two groups migrating toward each corner of 

 the square unite to form a single nucleus, so that from the eight groups there 

 result only four nuclei, one to each aster. There are many variations from this 

 more typical condition. Instead of a tetraster there may be a pair of parallel 

 amphiasters, and according as the corresponding asters of these amphiasters 

 are more or less intimately joined by their sarcodic rays, the condition of the 

 tetraster will be more or less closely approached. This is followed by a corre- 

 sponding segmentation into four spheres, which resemble in position the condi- 

 tion after the second normal cleavage. So at subsequent stages there are eight 

 instead of four spherules, etc. In the planula stage the larvae are irregular. 

 The formation of a tetraster, and the division into four spheres at once, the 

 author thinks, is not simply an abbreviation of events ; it is a more funda- 

 mental alteration of the normal process. 



Where there remain male pronuclei which have not become fused with the 

 female, (in cases where several spermatozoa have penetrated the yolk,) sooner 

 or later each of these male pronuclei is resolved into an amphiaster, from which 

 two nuclei arise. When two or three of the male pronuclei have united with 

 a corresponding number of the components of the female pronucleus, and there 

 are others which remain distinct, the conjugated nuclei give rise each to a 

 tetraster, and the superfluous male pronuclei also divide, but with less regu- 

 larity. All eggs embracing independent male asters are very irregular in their 

 segmentation. All those which have received more than one spermatozoon give 

 rise to at least twice as many segmentation spheres as would exist in a normal 

 embryo of the same stage of development, and become monsters. This mon- 

 strosity consists in the repetition of a primitive organ which should normally 

 remain single. Other results have already been given at pages 484 and 491. 



Fol, rejecting the term " deutoplasm," introduced by Ed. van Beneden, pro- 

 poses to distinguish the nutritive substances accumulated in the viteUus from 

 those often deposited by the embryo in its interior, and to designate the former 

 as ^' protolkithe" the latter as '^ deutolecithe.'' 



■ He proposes further to preserve the term membrane only for the thin layers 

 v/ith double contour, which are harder and more resistant than the protoplasm, 

 and which have lost the ability of remingling themselves directly as living 

 substance with the living protoplasm. He would class under the name of 

 limiting or plastic layers {couches limitantes or plastiques) those which have the 

 peculiarity of following the sarcode in all its changes of form, even the most 

 extreme, and of re-entering directly into the protoplasmic circulation, together 



