188 



BULLETIN' OF THE BUREAU OF FISHERIES. 



a. Spermatozoon. Note oval head bearing conical protuberance (at base of which are two doubly refractive bodies) and 

 long, slender tail. X 1.185. 



b. Ovarian egg removed from mantle. Imperfect sphere with an external membrane. Germinative vescicle with large 

 nucleolus visible. X 375. 



c. Ovarian egg slightly crushed under cover glass showing escaping nucleus and yolk granules. X 375. 



d. Ripe egg immediately after being shed. No definite form. Germinative vescicle has disappeared. X 375. 



e. Egg a few minutes after fertilization. Perfectly spherical. Spermatozoa acting against it cause it to roll about. X 45°' 

 /. Egg 20 minutes after fertilization, showing protrusion of first polar body. X 375. 



g. Egg 10 minutes later, showing appearance of second polar body just below first. X 375. 



h. Another egg showing a stage 5 minutes later. The two polar bodies are distinctly separated from egg proper which has 

 now become elongated. Cytoplasmic border at vegetative pole is beginning to take on an irregular outline and to withdraw 

 from cell wall. X 375. 



i. Egg 2 minutes later, showing increased activity at nutritive pole. Wavy outline of cytoplasm is more pronounced. 

 Cell membrane opposite to it is wrinkled and beginning to draw away from egg. X 375- 



j. Egg 10 minutes later, showing continued protuberance of nutritive pole, contents of which become more transparent than 

 rest of egg. Male pronucleus, MP, clear spot near nutritive pole; female ptonucleus, FP, similar body hear formative pole. 



X 375- 



k. Egg 10 minutes later. Unsymmetrical pear form. Pronuclei have fused and disappeared. X 375. 



/. Egg 2 minutes later. Pear form more symmetrical. Nutritive pole contains finer granules, and is therefore more trans- 

 parent. X 375- 



