212 THE FROG CHAP. 



insert the small scissors into the vent, and slit open the 

 cloaca very slightly to one side of the middle line, so as not 

 to injure the connection between it and the bladder. Notice 

 the openings into the bladder and large intestine respectively, 

 and also : 



In the male, the apertures of the ureters (urinogenital 

 ducts) , situated on two small papillae, lying close to one 

 another on the dorsal side of the cloaca : insert a bristle 

 into the ureter. Sketch. 



In the female, the two small apertures of the ureters, and, 

 just in front of these, the two large apertures of the oviducts, 

 all situated on the dorsal wall of the cloaca. Insert bristles 

 into the ureter and oviduct. Sketch. 



Impregnation and Development. 



In the early spring (end of February or beginning of 

 March), look about in ponds and ditches for frogs which 

 have taken to the water for the purpose of laying eggs. 

 This process can be watched more conveniently by catching 

 a few frogs, male and female, and putting them in a large 

 vessel of water or aquarium. If you have been unsuccessful 

 in procuring frogs or frogs' spawn, toads will do equally 

 well : their eggs are laid a few weeks later, and are arranged, 

 each surrounded by its gelatinous envelope, not in clumps, 

 like those of the frog, but in a string, like the beads on a 

 necklace. 



For purposes of observation, the spawn is best kept in a 

 glass vessel, together with some water-weeds. Put only a 

 small quantity of spawn in one vessel ; if the water begins 

 to get foul, change it at once. Examine the eggs every day 

 with a magnifying-glass or better, a low power binocular 

 microscope as development proceeds, and keep some of the 

 tadpoles alive until metamorphosis takes place in June. 



If you wish to see some of the stages in the development 

 of the frog during other times of the year, you must obtain 

 some preserved eggs and embryos, and, if possible, you 

 should also examine the series of wax models, made on an 

 enlarged scale, which are to be seen in most zoological 

 museums. 



The following are some of the more important things to 

 be noticed. (Sketch a series of stages) : 



Before hatching. 



I. The unsegmented oosperm. black above, and white 

 below. 



