262 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



furrow (fig. 26), or a sharp furrow (fig. 25), or a broad furrow with 

 a sharp angle (fig. 40). 



How widespread in the animal kingdom this very simple type 

 of cell-division may be is not entirely clear. Such cells as eggs 

 which occur free in the medium, lend themselves much more 

 readily to cell-division studies than do cells of tissues, such as 

 cartilage, muscle, etc. They are also of greater interest from a 

 reproductive standpoint, and hence it is no wonder that most of 

 our knowledge of animal cell-division is based upon the observa- 

 tion of such cells. In the minds of many zoologists there has 

 not Ipeen an adequate distinction between the processes of nuclear 

 and cell-division. Rabl in 1885 published his paper entitled 

 "Ueber Zelltheilung" (54), which devotes only two paragraphs 

 to cell-division proper, and over 100 pages to karyokinesis. This 

 simply serves to indicate the place of secondary interest to which 

 cytokinesis had been relegated. 



None the less, a vast amount of effort has been expended in 

 attempting to find some equivalent in animal cells of Strasburger's 

 beautiful and clean-cut figures of cell-division in the higher plants. 

 Hofmann (31) in 1898 published an excellent review of the litera- 

 ture bearing on the existence of a cell-plate in animals, and adds 

 some interesting observations on hydroids and Limax. He 

 deliberately chose animal cells which were imbedded in a matrix 

 having a high coefficient of viscosity and a low coefficient of 

 elasticity, so that the external conditions would closely simulate 

 those of most plants. There can be no doubt that he found 

 equatorial differentiations, as had Flemming and others before 

 him; but whether these should be considered homologous to the 

 cell-plate of the higher plants is not entirely certain. Unfortu- 

 nately, his preference for the iron-haematoxylin stain makes com- 

 parison with the leading botanical investigations difficult. No 

 orange zone is reported such as Timberlake found in the onion. 

 Only one figure of Limax and one of Tnitta show an inflated spindle; 

 whereas many figures of all species studied present an hourglass- 

 shaped spindle. There are only a few cases noted of granules 

 fusing to form a plate, in most instances the granules remaining 

 quite distinguishable. Several cases show a large globular 

 zwischenkorper; and none show a centrifugal si)litting of the 

 plate. The present tendency among reinitable zoologists is to 



