MUSEUM OF COMPARATIVE ZOOLOGY. 455 



and satisfactory a manner indicate — a transmigration of recognizable 

 morphological fragments of that substance. If, on the other hand, one 

 were to maintain that dissolved portions of the nuclear substance first 

 escaped the limits of the nucleus (and germinative vesicle), and then 

 were re-collected and thus gave the initiative to the protoplasmic asters, 

 it would be as impossible, with our present means of investigation, to 

 refute as to prove the claim. 



A short pause ensues — to return to Hertwig's description — after the 

 formation of the first maturation spindle. The formation of the polar 

 globules follows as in Nephelis. Two points only are of further interest : 

 first, that Hertwig noticed furrows on the surface of the polar globule, 

 as well as of the egg, which converged toward the place of constriction 

 during the budding process, and that the spindle before the formation of 

 the globules becomes broader and shorter. 



The possibility of an indirect formation of the second maturation 

 spindle, which Hertwig emphasized on a former occasion, neither finds 

 support nor opposition here. The fact that the inner aster has been 

 converted into a " Doppelstrahlung " within a quarter of an hour after 

 the formation of the first polar globule, would seem to preclude the 

 possibility of such an event in the case of the starfish. Nevertheless, I 

 think this point is worthy of still further examination. 



A zone of granules occupies each of the polar globules ; a third, says 

 the author, lies near the surface of the yolk. From the latter is formed 

 the Qgg nucleus, — just how is not quite evident. In the clear space which 

 these granules occupy there appear later a number of vacuoles, and in 

 the centre of each a granule of nuclear substance. The vacuoles soon 

 become confluent, thus forming the e^g nucleus, and later the granules 

 are united into a single structure,"* — the nucleolus. The egg nucleus 

 has moved during its formation toward the centre of the egg. Hertwig 

 does not say whether the stellate condition which the protoplasm " nach 

 dem Centrum des Eies zu " has assumed goes in advance of the vacuole 

 or not. It ultimately becomes fainter, and disappears. Hertwig did 

 not succeed in verifying Greeff 's observations of the parthenogenetic 

 development of the starfish. 



Calberla ('78, pp. 438-447) has ascertained that, accompanying 

 the metamorphosis of the Ammocetes stage into the adult form of Pe- 

 tromyzon Planeri, the germinative vesicle of the ovarian egg undergoes 

 a very slow migration to the surface of the yolk, and a metamorphosis 



* In the preliminary paper ('77", p. 274) it is stated that a single nucleolus arises, 

 after the vacuoles have become confluent, by an "Ausscheidung." 



