MUSEUM OF COMPAEATIVE ZOOLOGY. 139 



in brief, that the object of amitotic division is the distribution of nuclear 

 material throughout the cytoplasm, with corresponding increase of nu- 

 clear surface. He considers it the final phase of a series of conditions 

 which begins with a simple lobed nucleus, and includes branched nuclei 

 of various degrees of complication. In support of this interpretation, 

 Chun lays stress on the statement that cell division, after an amitotic 

 division of the nucleus, has seldom or never been observed with cer- 

 tainty, thereby implying that amitosis cannot have in view the multi- 

 plication of cells. I do not consider this as essential to the hvpothesis, 

 nor, in fact, do I believe him correct on this point. The evidence of 

 cell division after amitosis seems to me abundant and conclusive. It 

 was observed by F. E. Schulze ('75) in Amoelxi polypodia; by Ranvier 

 ('75), Biitschli ('76), Flemming ('82), Arnold ('87), and others, in leu- 

 cocytes; by Ktikenthal ('85), in the lymphoid ceUs of Annelids; and by 

 Camoy {^$>o), in various cells of Arthropods. As the foregoing shows, 

 there is abundant evidence that, in the serosa of the scorpion, division 

 of the cell sometimes, at lea^t, follows amitotic division of the nucleus. 

 Furthermore, the extremely regular and well ordered manner in which 

 the nuclei divide, and the similarity as to size and shape of the daughter 

 nuclei, seem to me decidedly against the notion that the sole object of 

 the division is to disseminate nuclear substance in the cytoplasm ; for 

 in those cases where amitosis is not followed by division of the cell, and 

 assumably takes place simply for the purpose of dissemination, the 

 nuclear products are very variable as to number, size, and shape. 



n. The Amnion. 



Plate I. Figs. 1 and 2 ; Plate II. Figrs. 16-30. 



The amnion is much thinner than the serosa, and like it is composed 

 of a single layer of flat, polygonal cells (Fig. 1, am.). But, while both 

 the cells and nuclei of the serosa have become enormously larger than 

 the blastodermic cells from which they originated, those of the amnion 

 have changed little as regards size. The boundaries of the amniotic 

 cells are not always visible, and I find that preparations, even when 

 hardened and stained in the same manner, show the greatest variation 

 in this respect. As a rule, the cell walls in the amnion are sharply and 

 clearly defined only in preparations of membranes from advanced em- 

 bryos. The same is true of the cell walls of the serosa. 



In general, the amniotic cell has but one nucleus, which usually occu- 

 pies the centre of the cell. Blochmann makes the same statement as to 



