22 



GENERAL ANATOMY OF THE TISSUES. 



Fig. 3. 



§ 11. 



The development of cells within other cells, or their 

 endogenous origin, is of very frequent occurrence, and easy to 

 be observed in embryos. The commonest form of this cell 

 genesis is, that a so-called parent cell produces two secondary 

 cells, which from the first wholly fill it. The first thing to 



be observed in this case, in the parent 

 cell, is a metamorphosis of its nucleus, 

 which grows, acquires two nucleoli, 

 becomes elongated, and divides into 

 r .5^Kr£)?\ ^ w0 - When this has once taken place, 

 A^'r^vi the nuclei become somewhat divari- 

 cated, and then a wall of separation 

 arises between the cells, which divides 

 the parent cell into two perfectly dis- 

 tinct spaces, each of which contains 

 a single nucleus and one half of the 

 contents. 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 possible, 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, marking the first trace of their 

 division, a median partition, which in favorable cases may be 

 recognised as composed 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, nothing 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 demonstrate with 

 certainty any endogenous development of nuclei ; so much the 



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, x 350. 



Fig. 4. An elongated nucleus, and one containing two secondary nuclei, from the 

 o\uni of an Ascaris dent at a, x 350. 



