344 BULLETIN OF THE 



The blood-corpuscles of the embryo fowl, on the fourth or fifth day of 

 incubation, when treated wdth reagents, furnish satisfactory proof that a 

 nuclear metamorphosis accompanies cell division. The so-called equa- 

 torial plate may in this case be composed of distinct rods, or may be an 

 actually continuous plate as in many plants. The spindle as a whole 

 is so large as to lead to the belief in an increase in the volume of the 

 original nucleus. Faint traces of a second equatorial thickening are 

 found and interpreted as a cell plate. 



Regarding the structure of the nuclei of blood-corpuscles Biitschli is 

 (p. 260) at variance with Auerbach (74, pp. 61-70, 98, 103, 114) inas- 

 much as he finds that the nuclear substance exists in the form of irregu- 

 lar fibres, with nodose thickenings in many places, which traverse the 

 nucleus and are united w^ith its envelope, rather than as discrete nucleoli. 

 The division of the white blood- corpuscles in Rana and Triton is accom- 

 panied by changes of the nucleus wdiich present only a remote re- 

 semblance to the typical metamorphosis of this structure. There is 

 simply an elongation of the nucleus, and a gradual swelling of its ends ; 

 w^hile the middle, connecting portion becomes attenuated to a fine 

 thread, which probably ruptures and becomes incorporated in the two 

 daughter nuclei. 



Strasburger's ('76, pp. 208-211) observations on nuclear division in 

 animal tissues were limited to studies on fibrous cartilage from the ear 

 of the calf. Notwithstanding the unfavorable nature of the object, — 

 preparations from which leave much room for the play of the imagina- 

 tion, — Strasburger believes the division takes place by the lengthening 

 of the nucleus, and the formation of an equatorial plate whose halves 

 separate and leave stretched between them "nuclear filaments," before 

 there is any sign of a division of the protoplasm. In the equator of the 

 nuclear [interzonal] filaments, and in the surrounding substance as far 

 as the wall of the cell, there is then seen a dividing layer, — the begin- 

 ning of the cell plate. This partition is not formed progressively from 

 the circumference inward, but is produced simultaneously throughout 

 its whole extent, and subsequently splits, as in plant-cells, into three 

 layers, of which the central forms the fibrous intercellular substance of 

 the cartilage. 



Studies by Eberth ('76), immediately induced by Strasburger's work, 

 and carried on without a knowledge of what Mayzel had done, corrobo- 

 rate most of the conclusions of the latter author. On the cornea of the 

 rabbit and the frog Eberth has also shown that after artificial removal 

 or destruction of the epithelium the ensuing regeneration affords oppor 



