224 CORA J. BECKWITH 



that this is the haploid number (figs. 39, 40, 46). A small element 

 near the center of the plate is characteristic. 



The spindle, still without asters or centrosomes, now rotates 

 95° until it is perpendicular to the surface, and then moves out 

 of the nuclear area toward the surface, where the first polar body- 

 is formed (figs. 43, 44, 45). As seen in some of the figures, a 

 single or double granular mass — the remains of the nucleus — is 

 left behind in the protoplasm, where it is absorbed. Since the 

 manner in which the tetrads are formed is not determined, it is 

 impossible to interpret this division in terms of reduction. The 

 second polar spindle is formed immediately, as shown in figure 46. 

 The egg is now shed from the gonophore, a small female germ 

 nucleus being very rapidly reconstructed from the remaining 

 chromatin (fig. 47) . The very great difference in size between this 

 nucleus and the germinal vesicle has been sufficiently emphasized 

 by previous writers on Hydi'oids. The egg, which has been some- 

 what flattened in the gonophore, rounds up when shed. 



This description of the formation of the first polar spindle 

 differs from that given by Smallwood, who finds it appearing with 

 asters in the protoplasm in connection with a very small nucleus 

 which is many times smaller than the typical germinal vesicle of 

 Hydractinia. The small size of the nucleus and the position of 

 the spindle outside of the nucleus makes it probable that he has 

 figured the first cleavage-nucleus and spindle. Since I have 

 traced consecutive stages in the breaking down of the germinal 

 vesicle and the formation of the chromosomes and spindle, 

 (stages which Smallwood lacked) it seems conclusive that a blunt 

 spindle minus asters and centrosomes lying in the center of the 

 large nuclear area, is typical for Hydractinia. This conclusion 

 is supported by the condition found in other forms, since a blunt 

 spindle minus asters has been described in a number of Hydroids 

 (Gonothyrea, Wulfert, '02; Clava squamata, Harm '02; Clava 

 leptostyla, Beckwith '09; Eudendrium, present paper; Linerges, 

 Conklin '08; Cordylophora, Morningstein '01; Cunina, Stschel- 

 kanowzew '06). Further the formation of the spindle within 

 the nuclear area itself also find support in the condition described 



