518 BULLETIN OF THE 



referable to the want of a uniform distribution of deutoplasm, — to the 

 polar concentration of the protoplasm, in other words 1 



If the pseudopodia are attributable to the same influence as that which 

 produces the stellate figures of the yolk, they may not of necessity be 

 the direct result of nuclear influence. But of this I shall speak more at 

 length when considering the nature of asters. In Hydra, they are 

 manifest during the first and second cleavage, — less prominently after- 

 wards. In osseous fishes, according to Oellacher and Van Bambeke, they 

 occur before fecundation.* Kupft'er and Benecke have described for 

 Petromyzon, beside more regular changes in the form of the primary 

 pole, a protrusion of clear protoplasm, which may be comparable with 

 the pseudopodia seen in other animals. According to these observers, it 

 is both connected with the elimination of the second polar globule, and 

 supplements the act of fecundation. Many observations, especially on 

 the Porifera by Haeckel and Schulze, tend to show the active amoeboid 

 condition of the growing ovum ; but in these cases the differentiation 

 of the primitive axis appears to take place comparatively late, so that 

 a direct comparison with later and more specialized manifestations is not 

 permitted. 



The entirely unique phenomena of " polar rings " (see Whitman, 78") 

 are in so far worthy to be classed here as they are special accumula- 

 tions of active protoplasmic (nuclear 1) substance, which manifest them- 

 selves soon after the formation of the polar globules. The "■ ring rays," 

 which stretch out from them toward the equator at the surface of the 

 yolk like the pseudopodal filaments of many rhizopods, and the final 

 migration of their substance inward toward the segmentation amphias- 

 ter, afford ample evidence of the active nature of their substance. But 

 how the dispersion of this substance in " ring rays " can be due to nuclear 

 attraction is not clear. 



The changes which have been observed at the secondary pole are not 

 numerous. The most interesting is that of the " aboral ring " and its 

 rays in Clepsine. The others are limited, so far as I know, to the 

 elevation of masses of active protoplasm, and their appearance is as 

 unaccountable as that of the aboral polar ring. 



By the figures which 0. Hertwig has given of this phenomenon in 

 Mytilus, one is reminded of the description which Bobretzky ('76; p. 102) 

 has given of the early stages of segmentation in Nassa ; and it may per- 

 haps be of significance in the study of these polar phenomena, that there 



* P. S. — As has been stated (p. 180), they may occur in species of Limax during 

 the formation of the polar globules. 



