GENERAL BIOLOGY 



tween the lamellae. (4) Canaliculi, minute dark lines radiating 

 from the lacunae. (5) Other lamellae are to be found not arranged 

 about canals, but filling in spaces not occupied by such systems. 

 Draw. 



VI. CONNECTIVE TISSUE. 



a. White fibrous tissue: (i) Tease out a bit of fresh tendon in 

 water; with a high power it is seen to be made up of fine wavy 

 fibres in bundles ; each fibre has faint outlines and does not branch. 

 (2) Treat with acetic acid; most of the fibres swell and become 

 invisible, but a few (yellow elastic fibres) and some elongated 

 granular connective tissue cells remain visible. 



b. Yellow elastic fibres : Tease out in acetic acid some of the 

 tissue immediately under the f rob's skin. Under a high power note : 

 Branched fibres with well defined outlines ; these may not be 

 found until several specimens have been examined. 



Draw both white and yellow fibres. 



D. EMBRYOLOGY. 



I. Early Cleavage Stages. Examine entire frog's eggs divided 

 into two, four, eight and sixteen cells. Note in the two-cell stage 

 that a grayish or slate colored area, crescentric in form, is present 

 on one side of the egg, and that it is, as a rule, bisected by the fi*rst 

 plane of cleavage. Note in the four-cell stage the relative dis- 

 tribution of the pigment on the anterior and posterior sides of the 

 egg. Note in the eight-cell stage the relative sizes of the upper and 

 lower cells, also the distribution of the pigment in the cells, and 

 the location of the grey crescent. Note in the sixteen-cell stage the 

 position of the planes of the fourth cleavage in the upper and lower 

 cells. Examine a section of one of the early cleavage stages ; note 

 the nuclei surrounded by pigment. Draw. 



II. Later Cleavage Stages. Examine two of the later cleavage 

 stages (Blastula stages). Note the comparative sizes of the cells 

 in the upper and in the lower hemispheres of the embryo. Examine 

 a section of a late cleavage stage. Note the large cleavage cavity ; 

 the thinness of the roof, and the thickness of the floor. Draw. 



III. Gastrula Stages. Study surface views of three gastrula 

 stages showing: (i)The beginning of the dorsal lip of the blasto- 

 pore, (2) the backward-growth of the dorsal lip, and the appear- 

 ance of the lateral lips, and (3) the formation of the ventral lip. 



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