xii PRACTICAL DIRECTIONS 211 



3. Examine under the microscope a transverse section of 

 the spermary, prepared as directed on p. 136, and note 

 (Fig. 62, A) the numerous seminal tubes or crypts which open 

 into it. Under the high power, observe the epithelial cells 

 (germinal epithelium) lining the tubes, and their subdivision 

 into smaller cells, which eventually give rise to the sperms, 

 the tails of which project freely into the cavities of the 

 tubes. Sketch. 



II. Female Organs. 



1. Notice again (a) the ovaries, varying in size and 

 appearance according to the time of year, and each sus- 

 pended by a fold of peritoneum : they are studded all over 

 with ovisacs, each of which contains an egg or ovum, pig- 

 mented when ripe ; and (b) the oviducts (Fig. 4). Trace the 

 convoluted and, glandular middle portion of the oviduct 

 forwards, and make out the anterior thin-walled portion, 

 running parallel to the gullet and opening into the ccelome 

 by a small aperture at the base of the lung ; then trace the 

 middle portion backwards, and notice the thin-walled, 

 dilated, posterior portion, which opens into the cloaca. 

 Sketch after examining the cloaca (see below). 



If a female frog is examined in the spring, just before the 

 eggs are laid, the ovaries will be seen to be reduced in size, 

 and the posterior portion of the oviduct filled with eggs, 

 each surrounded with a gelatinous coat secreted by the 

 middle portion. 



2. Examine under the microscope a section of the ovary, 

 prepared as directed on p. 136, first with the low, and then 

 with the high power (Fig. 63). Note the epithelial cells 

 (including the germinal epithelium) forming the walls of the 

 ovary, and the ovisacs in different stages of development. 

 Each ovisac contains an ovum, surrounded by follicle-cells. 

 In the ova, note the protoplasm and its contained yolk- 

 granules, the nucleus, and the nucleoli. Sketch. 



Cloaca. 



Carefully cut through the pelvic symphysis in the middle 

 line with a scalpel and press apart the two innominate 

 bones, so as to expose the ventral surface of the cloaca. 

 Inflate from the vent, and note that the large intestine is 

 continuous with the cloaca and that the urinary bladder 

 opens into it on the ventral side. 



The entire urinogenital apparatus, together with the 

 cloaca, may now be removed from the body, first cutting 

 through the skin round the vent. Pin down under water, 



P 2 



