No. 2.] DEVELOPMENT OF MARINE ANNELIDS. 27 1 



spending cells of the other quadrants is greater in Scolecolepis 

 than in any other form I have studied, Fig. 114 (shaded nuclei). 

 For example, d"^ is the largest cell in the &gg, d'^, V'^, c^'^ are 

 the smallest even more minute than the primary trochoblasts. 

 They corresponc in origin to the secondary trochoblasts in Ani- 

 phitrite and Clymenella. This diminutive size of the primary 

 and secondary trochoblasts is significant in view of the sup- 

 pression of the trochophore in this form. 



Owing to the lack of material, I made only the following ob- 

 servations : an apical rosette is formed in the ordinary manner; 

 a typical gastrula stage with elongated blastopore is present 

 somewhat later ; the elongated trochophore has a weak proto- 

 troch and paratroch ; the head segment is composed of clear 

 cells, and contains four unicellular mucous glands lying in a 

 row in front of the mouth, while the body segments are filled 

 with yolk and covered with a layer of epithelial cells (Figs. 

 115, 116). 



E. CH^TOPTERUS PERGAMENTACEUS cuvier.* 



The eggs of this rare annelid were obtained in August, 1 894, 

 by cutting open the females, and were artificially fertilized with 

 sperm obtained from the male in the same manner. 



The egg, which is about equal in size to that of Lepidonotus, 

 remains with the first maturation spindle in the equatorial-plate 

 stage, until the entrance of the sperm, as in Clymenella. The 

 male pronucleus reaches a position near the center of the egg 

 without following any constant path, and there awaits the 

 female pronucleus. The latter moves toward it along the radius 

 of the &g% which terminates at the polar globules. Before the 

 pronuclei unite, the two centrosomes derived from the sperm 

 center are already far apart, one on either side of the male pro- 

 nucleus. Their position indicates the direction of the first 

 cleavage spindle, since a line connecting the two centrosomes 

 coincides with the axis of the spindle. This is perpendicular to 

 the copulation path of the pronuclei, i.e., the &gg axis. It follows 

 that the horizontal plane in which the cleavage spindle will lie 



* For maturation and fecundation, see Mead.^* 



