STRUCTURE.] CELL-FORMATION. 31 



scales were isolated and brought under the microscope ; the 

 hairs which fringed the margin of the scales were thus 

 presented free throughout their whole length, and being very 

 transparent, afforded an admirable opportunity of examining 

 the cells in their different stages in a perfect and uninjured 

 condition, an important point which cannot be secured in 

 sections of growing tissues. In the earliest stage the nuclei 

 were perfect and distinct one from another ; in the next, the 

 transverse lines indicate the commencement of the infolding 

 of the primordial utricle; that the lines are not septa is seen 

 by the appearance of hairs which had been kept in spirit 

 several days ; in these, the primordial utricle, detached from 

 the lateral walls, is continuous throughout the whole length of 

 the hair. Different stages of the infolding, that is, the 

 progress of the fold towards the centre, are shown by the 

 constrictions exhibited by the coloured mucilaginous cell- 

 contents. In a specimen treated with iodine, the septa were 

 incomplete in the upper part of the hair, but the lowest 

 septum was perfect the primordial utricle with the cell- 

 contents having become retracted from it. In this septum 

 two new layers may be traced from the lateral walls, 

 intimately united toward the centre, so as to appear like 

 one layer. This example also showed that the layers forming 

 the septum are continuous with a new layer deposited over 

 the inside of the lateral wall. Mohl states that each layer of 

 new matter grows from the circumference to the centre, and 

 that the septum is not produced by a succession of layers ; 

 each projecting a little beyond that preceding it. This point 

 I have not yet been able to determine for myself. In the per- 

 fect cell, the primordial utricle, with the nucleus, undergoes 

 dissolution/' (Annals of Natural History, vol. xviii. p. 367.) 

 " These views, however," adds Mr. Henfrey, " which I have 

 adopted of the nature of the process of multiplication by 

 division, are not sufficient to explain all cases of cell-develop- 

 ment, I allude particularly to the production of free cells in 

 the cavity of a parent cell, such as occurs in the formation of 

 spores and pollen. Supposing that this is not effected in the 

 way described by Schleiden, namely, by development from 

 nuclei, it is necessary to suppose, either with Nageli, that the 



