414 VERTEBRATE LIFE AND ORGANIZATION 



Figure 21.16. Leopard frogs in amplexus. 



ducts, the vasa efferentia, which cross to the anterior portion of the 

 kidney in the mesentery supporting the testis. The vasa efferentia con- 

 nect with certain of the kidney tubules through which the sperm pass 

 to the Wolffian duct. The sperm may be stored briefly until mating in a 

 slight enlargement of the Wolffian duct known as the seminal vesicle. 

 Certain of the kidney tubules and the Wolffian duct thus have a dual 

 function in the male— the production and transport of urine, and the 

 transport of sperm. 



Male frogs often have vestigial oviducts lying beside the Wolffian 

 ducts. These are remnants of a sexually indifferent stage of the embryo 

 when rudiments for both male and female systems are present. 



During mating, the male grasps the female about her trunk with 

 his forelimbs, an embrace termed amplexus (Fig. 21.16). Then, as the 

 female discharges eggs into the water, the male sheds sperm. Fertiliza- 

 tion is external. As the eggs are laid, the protective layers of jelly imbibe 

 water and swell. 



190. Sense Organs 



The survival of an organism requires that it respond stiitably to 

 changes in the environment. This entails the perception of changes in 

 the internal and external environments, the integration of this in- 

 formation, and the stimulation and coordination of appropriate effectors 

 —muscles, glands, cilia and chromatophores. Although some sensations, 

 such as pain, are detected by free nerve endings, most stimuli are re- 

 ceived by special cells or groups of cells, called sense organs, or re- 

 ceptors. 



Receptors for touch, pressure, temperature changes, and the like 

 are widely scattered, but those for smell, taste, light, sound and equi- 

 librium are usually aggregated. The receptors for smell are collected in 

 a special olfactory epithelium lining part of the nasal cavities. Those 



