EMBRYOLOGY. 

 FBOG. 



I. Two-, four-, and eight-celled stages.* 



Study in a watch-glass with a hand-lens. Do 

 not touch the eggs ; if it is necessary to turn 

 them over, do so with a stream from a pipette or 

 roll them over ly tipping the watch-glass. 



Make three sketches of each stage : 



1. From the dark pole. 



2. From the light pole. 



3. From the side half-way between 1 and 2. 



II. Gastrula, surface view. Three stages. 

 Examine as in I. 



Note the formation of the blastopore. 

 Sketch. 



III. Blastula. Prepared section. /Sketch. 

 Study with microscope. 



IY. Gastrula. Prepared section. Sketch. 



Study with microscope. 



Y. Closure of the blastopore and the formation and 

 closure of the medullary folds. Two stages. 

 Sketch. 



Study in a watch-glass with a hand-lens. 

 VI. The appearance of the adhesive glands, the eyes, 

 the nasal pits, the mouth, and the gills ; and 

 the formation of the operculum. Four stages, 

 Sketch. 



* When preserved in a dilute aqueous solution of formic alde- 

 hyde (1-2 per cent., see page 95) the egg-membranes retain their 

 transparency and the egg has a perfectly normal appearance. 



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