464 BULLETIN OF THE 



wise, a gamic cell-generation is followed by a line of agamic generations 

 the last of which are the small cells called by Robin polar globules. 

 With the production of these globules we arrive at the sexually ripe egg. 

 In accordance with all this, I interpret the formation of polar globules as 

 a relic of the primitive mode of asexual reproduction, which normally pre- 

 cedes fecundation, and is therefore no part of the process of impre^ma- 

 tion. This interpretation accounts for the otherwise inexplicable fact 

 that amphiastral divisions of the nucleus introduce the formation of the 

 directive cells, and is in harmony with the absence of such cells in Infu- 

 soria, and their general occurrence among plants and animals." 



The subject of "polar rings" is considered in connection with that of 

 pronuclei, and both are reviewed farther on. (See p. 503.) 



The second of the papers by 0. Hertwig ('78") of which a synopsis 

 was published in 1877 contains the results of studies on coelentrates, 

 worms, echinoderms, and mollusks. Among the coelentrates the uni- 

 nucleolar is the prevailing but not the exclusive condition of the germi- 

 native vesicle. As in Asteracanthion the nucleolus is composed of two 

 substances of different refractive power. The eggs of ^ginopsis and 

 Mitrocoma when excluded are naked and agree with Toxopneustes in the 

 early formation and loss of the polar globules, which can be found only 

 by the study of eggs taken from the ovary. In Pelagia and Nausithoe 

 there are two or three polar globules, which are retained in contact 

 with the yolk by the gelatinous mass in which the eggs are laid, and 

 which contain one or several nucleolar structures. If three globules 

 are formed, the third arises by a division of the one first formed. All 

 the eggs which are ripe and excluded into the sea-water already possess 

 before fertilization a small homogeneous egg nucleus at the surface of 

 the yolk. 



Of the Siphonophorse the eggs of both Physophora hydrostatica and 

 Hippopodius gleba exhibited each two polar globules, mistaken by P. E. 

 Miiller in the case of the latter genus for spermatozoa. 



Among the Ctenophorse, Gegenbauria cordata exhibited constantly two 

 polar globules, at some little distance from an egg nucleus which lay at 

 the boundary of the yolk granules and cortical layer of protoplasm. A 

 third body like the polar globules was occasionally seen a little distance 

 from the latter, but why he should suggest that it might be a sperma- 

 tozoon rather than a third polar globule, I do not understand. 



The germinative vesicle of the immature eggs of Sagitta is peculiar in 

 having, instead of a single large nucleolus, a number of smaller nucleoli 

 which lie on the membrane of the vesicle. Also a reticular substance is 



