450 BULLETIN OF THE 



tion — especially the phenomena of conjugation — among the lower 

 organisms, 



A critical review of Biitschli's " Studien," etc., by Dallinger and 

 Drysdale ('77). is principally directed to pointing out what is obser- 

 vation and what inference in Biitschli's work. 



Hatschek ('77"), without having devoted especial attention to the 

 phenomena of maturation in Pedicellina echinata,.has observed (p. 504) 

 the existence of two or three (1) polar globules of variable size, which 

 are found at the animal pole of that axis which he believes is differen- 

 tiated in the unsegmented eggs of all Metazoa (p. 524). A definitely 

 limited nuclear structure nearer the animal than the vegetative pole 

 (which may be the primary cleavage nucleus) is the centre of a radial 

 arrangement of the yolk elements. 



The maturation changes of the eggs of Malacobdella and Clepsine 

 have been incompletely observed by Hoffmann ('77, pp. 18-21, and 

 '77", p. 34). In the former case the germinative vesicle in approaching 

 the surface gradually diminishes in size, but preserves its rounded out- 

 line. Two hours after fertilization two polar globules were seen. 



With the growth of the egg of Toxopneustes variegatus there appears 

 according to Selenka ('78 and '78") a remarkable differentiation of the 

 cell into three concentric layers. The middle is a very thin pellucid 

 layer of protoplasm without granules, and disappears when the full size 

 is reached. During the later stages of growth, the outer yolk layer sends 

 out pale pseudopodia, which, at first isolated, arise as blunt or bush-like 

 projections of rapidly altering form, but finally assume the shape of very 

 numerous and fine, motionless rays. These, he believes, serve for the 

 growth of the egg. The whole yolk is undergoing change of form dur- 

 ing the activity of the pseudopodia. Finally it comes to rest, and the 

 pseudopodia are withdrawn. Meantime the germinative vesicle has suf- 

 fered changes from its spherical form ; its membrane has been variously 

 folded and wrinkled ; it has approached the periphery of the yolk after 

 the resorption of the germinative dot. Two polar globules are formed. 

 The place of their formation remains a long time recognizable as an 

 elevation of the surface of the yolk (Dotterhiigel). There then appear 

 in the yolk under this elevation several clear bodies which unite to form 

 the " Eikern." The latter moves inward, but does not take a central 

 position in the yolk. It is probable that the " clear bodies " are the 

 product of a budding (Abschniirung) of the germinative vesicle. 



The comparison which Strasburger previously ventured to draw be- 

 tween polar globules and the " Bauchkanalzelle " of the higher crypto- 



