5. OVULATION AND EGG TRANSPORT 



DEFINITION: A study of the process by which the egg is released from the ovary and is 

 carried to the uterus. 



PURPOSE: To become acquainted with the changes in the egg that occur between its hi- 

 bernation environment in the ovary and its delivery into the chamber (the uterus) for 

 oviposition, and to study the functions of the various parts of the reproductive tract 

 of the female in relation to the preparation of the egg for insemination. 



MATERIALS: 



Biological : Mature frogs, male and female (Rana pipiens). 



Technical : Dissecting instruments; hypodermic syringe and #18 needle; wide-mouthed 

 pipettes; finger bowls, Syracuse dishes, Petri dishes, stenders, Standard 

 (Holtfreter ' s) Solution. 



METHOD: 



Precautions : The ovulating female must be studied at the height of sexual activity, 

 before all of the eggs have reached the uteri. The opened body cavity should be 

 kept moist with Standard Solution. 



Control : No control is possible for this type of experiment for it is a matter of ob- 

 servation of a normal process. 



P r o c e du r e : Induce ovulation in a female Rana pipiens in the usual manner (see 



"Induced Breeding") and keep the frog at a laboratory temperature of about 23° 

 to 25° in a small amount of water. Test in 1 6 to 24 hours for the presence of 

 eggs in the uteri and exainine every 6 hours, or less, thereafter until eggs begin 

 to appear. Within 2 to 3 hours after the appearance of the first eggs in the uteri, 

 the following observations are to be made. 



Cut off the head of the frog and remove its appendages, leaving the torso. Avoid 

 unnecessary squeezing of the body. Lay the torso on a biologically clean cork 

 dissecting board or on paper towelling and open the abdomen from the pelvic 

 girdle to the xiphisternum, avoiding all parts of the genital tract. Cut aaay a 

 large piece of the ventral abdominal wall, including the peritoneum, and pin it 

 down (inverted, with peritoneum uppermost) to Permoplast in concentrated 

 Standard Solution in a Petri dish. Pin back the abdominal wall and remove the 

 viscera so as to expose the entire reproductive tract. With a pipette add about 

 5 to 1 cc. of Standard Solution to the body cavity and suck out any blood clots. 



THE OVARY 



Remove one ovary completely and place it in Standard Solution in a finger bowl shielded 

 from all heat. Examine with the naked eye and then under low power rnagnification. 

 Identify the following: 



a. Lobes of the ovary - how many are there? 



b. Movement of the ovarian lobes - how frequent; can movement be stimulated; is 

 it the smooth or striated muscle type of movement? Do the lobes move simul- 

 taneously or separately? 



c. Egg follicles : Locate an egg emerging from its follicle. Is the emergence slow 

 or rapid; is it accompanied by a flow of fluid or blood; do all eggs emerge simul- 

 taneously; do any eggs rupture into the cavity of the ovary; are the eggs in any way 

 distorted as they emerge from their follicles? (See papers by Rugh 1935: Jour. 

 Exp. Zool. 71:163.) 



