62 PROCEEDINGS OF THE AMERICAN ACADEMY 



blastic nuclei in the process of division. Hoffmann admits that his 

 observations are not complete, inasmuch as he was unable to follow 

 the division of the first cleavage-spindle, and did not even find a 

 spindle formation for the original parablastic nucleus. His failure in 

 these particulars is attributable to his method of employing strong 

 acetic acid (five to ten percent), which renders the germinal disc 

 opaque so rapidly that one can get only uncertain glimpses of what is 

 going on in the interior. Mounted preparations, or actual sections of 

 these early stages, would have given pictures of a much more reliable 

 character, wiiich would have served to confirm or correct impressions 

 obtained by the acetic acid method. After reading carefully Hoff- 

 mann's account of the initiatory cleavage, we find that the following 

 questions have been left either unanswered or in uncertainty : — 



(1.) Does the supposed horizontal cleavage take at first the form of 

 a circular groove ? 



(2.) What are the form-changes which accompany this cleavage? 



(3.) Does the vertical axis of the blastodisc lengthen or shorten 

 during the process ? 



(4.) Can the primary periblastic nucleus be demonstrated either by 

 actual sections or mounted preparations? 



(o.) Can any parallel for such a cleavage be found in any other 

 class of animals? 



With reference to the first question we are told, — " Das Ei von 

 Scorpaena ist, im Vergleich zu den gewohnlichen Zellen immer eine 

 sehr grosse Zelle, und es wird also eine geraume Zeit dauern, bevor 

 die Furche, welciie alsbald Archiblast und Parablast vou einander 

 scheiden soil, so tief vorgedrungen ist, dass wirklich vullige Trennung 

 beider Stiicke folgt. Bevor es hierzu konunt, hat sich der erste Kern 

 des Archiblast, und wie mir hochst zvahrscheinlich tst, auch der dcs 

 ParaMast, schon wieder in eine neue Spindel umgehildet." 



Neither the figures nor the descriptions give us any very definite 

 idea of the time or the manner in which this remarkable cleavage takes 

 place. About the time the two primary nuclei (one of the archiblast, 

 the other of the parablast) appear, we are informed that the blastodisc 

 changes from a biconvex to a plano-convex form ; but whether this 

 change accompanies the division of the first cleavage-spindle, or fol- 

 lows it, is left entirely to conjecture. Certainly there is nothing in 

 such a change which would imply a lengthening of the vertical axis 

 of the blastodisc ; nor does it follow with certainty that the axis 

 shortens. There is then, confessedly, a great deal of uncertainty in 

 regard not only to details, but also to some of the more important 



