i6o Papers from the Marine Biological Laboratory at Tortngas. 



complex and spectacular processes of mitosis." No confirmation of such 

 a view can be found in the egg of Linerges, where both maturation spindles 

 may be seen in eggs stained and mounted entire, as well as in sections. 



First cleavage. — The egg nucleus remains near the maturation pole and 

 the sperm nucleus migrates up through the egg until it comes to lie just be- 

 neath or alongside of the egg nucleus (figs. 5, 39). The cleavage amphi- 

 aster then arises, but I have not observed the details of its origin. The 

 chromosomes are then divided in the usual manner and the daughter nuclei 

 are formed by the fusion of chromosomal vesicles (fig. 6). In the telophase 

 of the division each of the daughter nuclei is sometimes composed of two 

 equal vesicles (fig. 7) which probably represent the halves of the egg and 

 sperm nuclei, the gonomeres of Haecker ( 1902). Chromosomal vesicles or 

 gonomeres are present in many of the later cleavages, but in no instance have 

 I seen any evidence that the nuclei ever divide by amitosis, as Child (1907) 

 and Hargitt (1904, 1906) suppose to be the case in other coelenterates. 



I have followed the cleavage in Linerges cell by cell to the 64-cell stage 

 and can affirm that up to this stage at least every cell divides by mitosis, 

 while mitosis is of very frequent, if not of universal occurrence in the later 

 divisions. In view of this fact it is needless to say that the case of Linerges 

 afifords no evidence whatever in favor of the view expressed by Hargitt 

 (1906) that nuclei arise dc novo during the cleavage of Eudendriuni, Pen- 

 iiaria, Clava, and perhaps of other coelenterates also. 



After the division of the nucleus the cell-body begins to divide in the 

 manner characteristic of the coelenterates. The peripheral layer is thicker at 

 the animal pole than elsewhere, as Ziegler (1903) in particular has shown 

 for the cten(iphore Bcroc. The cleavage-furrow begins at this point and 

 slowly cuts through the egg to the vegetal pole. The advancing edge of the 

 cleavage-furrow (or "cleavage-head") is always rounded, and as the walls 

 of the furrow come together behind this edge there is left a hole through 

 the egg. In the earlier stages of cleavage this hole is elongated in the direc- 

 tion of the cleavage plane (figs. 8, 9, 15, 16) ; in later stages, as the hole ap- 

 proaches the periphery it becomes elongated at right angles to the cleavage 

 plane (figs. 10, 11, 17, 18). As this advancing furrow approaches the vege- 

 tal pole the yolk is pushed aside and the peripheral layer of protoplasm from 

 the animal pole comes into contact with that of the vegetal pole, leaving 

 a connecting strand or bridge of protoplasm between the 2 blastomeres at 

 the vegetal pole (figs. 11, 12). It frequently happens that after nearly 

 reaching the vegetal pole the hole or cleavage head turns to one side (fig. 

 11), probably owing to the streaming of protoplasm through the bridge from 

 one cell to the other. In this way the furrow may be turned to one side, and 

 the daughter cells become unequal (fig. 13). 



Sections of the egg before this cleavage is finished show a large cavity 

 within the egg along the line of the cleavage-furrow (figs. 40-43). This 



