422 BULLETIN OF THE 



(3.) The surface of the egg in Strasburger's Fig. 2 is slightly elevated 

 in the region of the questionable corpuscle, somewhat as in Figs. 43 and 

 50 of Limax. 



I am well aware that serious objections to this view of the matter 

 may be raised. The entire absence of anything which could answer to 

 the spindle itself, the thickenings of its fibres, or the deeper sun, is at 

 first thought a weighty objection, and yet I can readily believe that in 

 eggs treated first with alcohol these structural peculiarities may have 

 been obscured by the opacity of the yolk, so that only those parts which 

 lay near the surface were distinguishable. Perhaps a more serious ob- 

 jection exists in the probability that the questionable corpuscles were 

 stained by treatment with osmic acid and Beale's carmine. Strasburger, 

 I believe, does not say directly that such is the case ; but even if it 

 was stained, I am not sure that on that account my explanation is to 

 be abandoned. Whitman ('78", p. 18) says of the "pellucid spot," in 

 the case of Clepsine, that it is deeply colored with carmine, and he too 

 made use of osmic acid. As far as regards this " pellucid spot," I think 

 I have reason to claim that it corresponds with the corpuscle in the 

 centre of the aster of Limax (a a'), and is not derived from the nuclear 

 plate which Whitman, it is true, did not see, but which could hardly 

 have divided and migrated to the tips of the spindle at so early a 

 stage as is represented by his Fig. 63, or, still less, at the stage of his 

 FW. 62. So far, then, I have indirect evidence that this flattened cor- 

 puscle may stain in osmic acid, and therefore am able to explain its 

 dark appearance in the figures given by Strasburger. I regret that 

 none of my preparations of this stage were made with osmic acid, as, 

 had they been, I might be able to add direct evidence of the staining 

 capacity of these areal corpuscles. 



If this explanation be correct, we may confidently expect that the 

 polar globules and their mode of formation will be soon made clear to 

 us in tunicates, and thus one more group of animals be made to lend 

 evidence in support of a rational explanation of the phenomena of matu- 

 ration which shall be applicable to all the higher animals, if not to all 



* P. S. — By the last paper of 0. Hertwig ('78", p. 191) my attention has been 

 called to a preliminary notice by Fol ('77*, p. 339), in which he mentions the exist- 

 ence of two polar globules in the case of Phallusia, that I had entirely overlooked. 

 The oversight was due to the incomplete manner in which the contents were indi- 

 cated on the cover of the magazine in which Fol's article is published. He has two 

 articles in the October number of the magazine, but his name appears only once on 



