MUSEUM OF COMPARATIVE ZOOLOGY. 521 



arises subsequently in this protuberance, I cannot think these radial ridges 

 are due to anything different from that which causes the true asters. 

 The appearance of one or both the asters seems, then, to be the first 

 change in the approaching metamorphosis. That is entirely consonant 

 with the observations made on the nuclear metamorphosis preceding the 

 first cleavage in Limax. It is certainly a matter of no great importance 

 whether the invasion takes place a little earlier or a little later in the 

 history of the formation of the asters. In Limax the asters are often so 

 far removed from the nucleus that they must attain considerable size 

 before any conspicuous changes are effected in the latter. In other cases, 

 as, for example, in the pteropods as shown by Fol, the earliest evidence 

 of the existence of a star is to be seen within the outline of the nucleus. 

 I do not conceive, however, that cases like the last really conflict with 

 the conclusions just stated. The transparency of the nucleus may be in 

 itself enough to explain the detection of rays through its substance sooner 

 than in the surrounding protoplasm. Fol's ('77^) account of the meta- 

 morphosis of the germinative vesicle in Asterias glacialis seems to indi- 

 cate that the asters arise at a much later period, namely, after radical 

 changes have taken place in the germinative vesicle and in the germina- 

 tive dot. It is without doubt one of the most delicate and difficult of 

 the questions connected with maturation, to ascertain when and where 

 the first traces of the archiamphiaster appear. But unless this author's 

 final paper brings strong evidence to show the inaccuracy of Hert wig's 

 observations, it seems to me we may accept the latter as entirely trust- 

 worthy in this particular. Certainly the figures accompanying Fol's pre- 

 liminary paper in no way invalidate the evidence given by Hertwig, for 

 in the earliest stage figured in which acids had been employed (Fig. 5) 

 not only are both asters formed, but the spindle is represented and also 

 its equatorial thickenings. But that condition represents a stage much 

 advanced beyond the first appearance of the first aster. The want of 

 evidence that asters exist in the stages represented by the figures which 

 precede may be due to their all having been made from living eggs. It 

 can scarcely be doubted, for example, that the stage shown in his Fig. 4 

 is more advanced than that exhibited in Fig. 5, since the oblique or tan- 

 gential direction of the spindle (Fig. 5) precedes rather than follows the 

 radial position (Fig. 4). Concerning the statement that the amphiaster 

 is formed within the germinative vesicle, or what remains of it, but is 

 from the beginning eccentric in position, I can only say that the drawing 

 (Fig. 5) is not sufficient to prove that the centres of the asters lie within 

 the finely granular territory which I take to be the remains of the ger- 



