768 DIRECTIONS FOR LABORATORY WORK 



(d) segmented spireme (Prophase stages). 



(e) chromosomes in equatorial plate (monaster figure) ; Meta- 

 phase stage. 



(f) some stage of the migration of the daughter chromosomes 

 (derived from a longitudinal splitting of the prophase mother 

 chromosomes) towards the poles (Anaphase). (The double 

 group of chromosomes of the anaphase stage is designated 

 the disaster figure.) (The achromatic spindle holding the 

 chromosomes is called the amphiaster.) 



(g ? h, i) three stages in the recoristitution of the nuclei of the 

 two daughter cells (Telophase) ; these are the same as the 

 prophase stages, but follow in inverse order. Note presence 

 of mid-body or cell-plate at anaphase. 



How do the two daughter cells resulting from a division differ in 



shape, and in the disposition of their major axis, from the mother cell ? 



Note changes in nuclear membrane ; formation of achromatic spindle 



(centrosomes are lacking in flowering plants) ; different position of 



chromosomes on spindle at metaphase and anaphase. 



(2) Make a similar series of drawings (25) of stages of mitosis in 

 the epithelial cells from sections of the skin of the tail of an amphibian 

 larva (e.g., salamander, frog). (Demonstration slide.) 



IV. HISTOGENESIS 



(1) Sketch (26) several phases in the segmentation of the egg of 

 the starfish, including the two and four cell (blastomere) stages. 



(2) Sketch (27) a transverse section of a vertebrate embryo (e.g., 

 frog or salamander larva), showing an early stage in the formation of 

 the germ layers. Label ectoderm, mesoderm, entoderm, notochord, neu- 

 ral groove (canal), somite, celom, and the primitive intestine. 



V. EPITHELIUM 



I. Simple (Non-stratified). 



(A) POLYHEDRAL (e.g., column of liver cells). 



The polyhedral represents the least modified type of cell, from the 

 standpoint of shape. The original or embryonic shape of all cells is 

 spheroidal. All the morphologic types of cells may be interpreted in 

 terms of a mechanically modified spheroidal cell. 



