140 THE FROG CHAP. VTTI 



noting the parts enumerated in each case, as well as the 

 structure of the nuclei (nuclear membrane, chromatin, and 

 nucleoli). 



1. Vertical Section of Skin (Fig. 38). 



a. Epiderm, stratified epithelium, divisible into outer 

 (horny] and inner (Malpighian) layers. 



b. Derm, connective-tissue fibres, blood-vessels and pig- 

 ment-cells. 



c. Cutaneous glands with their ducts. The apertures of 

 the ducts on the surface you will probably have noticed 

 already in your preparation of the epithelial cells of the 

 skin (p. 124). 



Sketch. 



2. Transverse Section of Intestine (Fig. 39). 



a. Mucous membrane : a superficial epithelial layer of 

 columnar cells, with goblet-cells amongst them ; and a 

 deeper connective-tissue layer, enclosing vessels and nerves. 



b. Muscular layer : an external longitudinal, and an 

 internal circular layer of unstriped muscular fibres. 



c. Peritoneal layer. This is very thin, and a careful 

 examination of good preparations is required in order to 

 make out its structure (p. 131). 



Sketch. 



3. Transverse Section of Stomach (Fig. 40). After recog- 

 nising the layers as above, note : 



a. The gastric glands, and b. the muscularis mucosce. 

 Sketch. 



4. Sections of Pancreas (Fig. 41). 



a. Lobules, separated by connective-tissue, and each 

 consisting of gland-cells with secretion-granules towards their 

 inner ends; b. ducts. 



Sketch. 



5. Sections of Liver (Fig. 42). 



a. Polyhedral gland-cells, arranged in columns ; b. bile- 

 passages and ducts ; c. blood-capillaries and vessels. 

 Sketch. 



