GENERAL EMBRYOLOGY 



1601 



brane of the corresponding daughter-nucleus. Two complete 

 daughter-cells are thus formed, and the telophase or concluding 

 stage is finished. 



The complex changes concerned in the mitotic division of the 

 parent-cell are concluded with the formation of two complete 

 daughter-cells. 



Summary of Karyokinesis, or Mitosis. — ^There are four phases 

 — namely, anaphase, metaphase, kataphase, and telophase. 



The anaphase consists in (i) the conversion of the linin — and 

 chromatin — reticulum of the nucleus into a spireme, or skein ; 

 {2) the breaking up of this spireme into chromosomes ; and (3) the 

 formation of a spindle from the spindle-fibres which connect the 

 two centrosomes, these centrosomes gradually separating from each 

 other, and the nuclear membrane disappearing. 



The metaphase consists in the congregation of the chromosomes 

 at the equatorial plane of the spindle. 



The kataphase consists in (i) the splitting of each chromosome 

 into two daughter-chromosomes, and (2) the migration of these 

 daughter-chromosomes from either side of the equatorial plane of 

 the spindle along the corresponding spindle-fibres to either pole of 

 the spindle where they enter the aster. 



The telophase consists in (i) the formation of a daughter-nucleus 

 within each aster, and (2) the cleavage of the cytoplasm of the 

 parent-cell into two halves, each of which sur- 

 rounds the corresponding daughter-nucleus, two 

 daughter-cells being thereby formed. 



Amitosis. — This is direct cell -division. The 

 nucleus is simply cleft into two daughter-nuclei, 

 and this is accompanied by cleavage of the cyto- 

 plasm. 



The Spermatozoon. 



The spermatozoon is the germ-cell of the male, 

 distinguished from the ovum, which is the germ- 

 cell of the female. 



A spermatozoon is essentially a cell, though it 

 has undergone considerable modifications from the 

 usual cell-type. It is an elongated body, which is 

 endowed with remarkable power of movement, the 

 movement being of a lashing or vibratory nature. 

 It consists of the following parts: 



I. A head. 2. A middle piece. 



3. A flagellum or tall. 



Fig. 658. — Sper- 

 The head is short, and, as seen on the flat, is matozoon. 

 oval. When, however, it is viewed in profile it 

 is pyriform, the narrow end being directed forwards. It is pro- 

 vided with a head-cap, which covers its anterior part. Over the 

 apical, somewhat pointed, anterior part of the head this cap is 



lOI 



Head 



-Middle. 

 Piece 



. FUgelluin. 

 or Tail 



■ Terminal 

 Filameut 



