50 



GENERAL ANATOMY OF THE TISSUES. 



it. The first thing to be observed in this case, in the parent cell, is a 



metamorphosis of its nucleus, which grows, ac- 

 quires two nucleoli, becomes elongated, and 

 divides into two. When this has once taken 

 •'^ place, the nuclei become somewhat divaricated 

 and then a wall of separation arises between 

 the cells, which divides tha parent cell into 

 two perfectly distinct spaces, each of which con- 

 tains a single nucleus and one half of the con- 

 tents. The mode in which the multiplication 

 of the nucleus takes place, has not yet been 

 made out with exactness. This much, however, 

 is certain, that where clear observation is pos- 

 sible, it is always the nucleoli which first divide into two and then diverge 

 a little. In the nuclei, which have at the same time slightly elongated, 

 there then usually appears, making 'the first trace of their division, a 

 median partition, which in favorable cases may be recognized as com- 

 posed of two secondary nuclei applied to one another by their flat sides 

 and completely filling the parent nucleus. Very frequently we see, in 

 the course of this process of multiplication of the nuclei, no- 

 thing more than, first an elongated nucleus, with a partition and 

 two nucleoli, and then two hemispherical nuclei applied by their 

 plane faces to one another, without its being possible to demon- 

 strate with certainty any endogenous development of nuclei ; 

 so much the less, as it is not to be doubted that, together with the latter 

 process, a multiplication of nuclei hy division takes place, in which an 

 elongated parent nucleus, with two nucleoli, breaks up into two by the 

 formation of a constriction which gradually deepens in the middle. 



The further destiny of the parent cells, with a partition and two 

 nuclei, is not always the same. As a rule, it appears that in each, two 

 perfect secondary cells afterwards become evident, which may serve as 

 a demonstration that the partition is double from the very first. At 

 other times, distinct secondary cells are not recognizable, which however 

 does not imply that there exists a mode of cell-development by the mere 

 formation of partitions, but only that in such cases the secondary cells 

 do not become distinctly separated from the parent cells. Whether the 

 one process or the other take place, it rarely stops at one performance, 

 but is generally repeated a certain, often very considerable number of 

 times ; in fact, as long as the organism grows. The parent cells either 

 remain, or they cease earlier or later to be histologically distinct struc- 



Fig. 4. 



Fig. 3. — From the cephalic cartilage of an advanced tadpole. Parent cells, with 1 and 

 2 nuclei, or 2-4 secondary cells, and some interstitial substance ; magnified 350 diameters. 



FiQ. 4. — An elongated nucleus, and one containing two secondary nuclei, from the ovum 

 of an Ascaris dentata; magnified 350 diameters. 



