104 AN INTRODUCTION TO ZOOLOGY 



Pituitary Body. 



The hypophysis cerebri or pituitary body is, as we have 

 seen, a saccular structure situated at the base of the brain inside the 

 cranium. It is complex developmentally arid histologically, but 

 includes a glandular portion of typical epithelial cells, whose internal 

 secretion influences the growth of the body. Disease of the pituitary 

 body leads to a very characteristic condition, known as Acromegaly 

 or gigantism the hands, feet, jaw and bony parts of the body 

 become much enlarged and exaggerated. The disease does not at 

 first lead to the destruction of the gland, but on the contrary to 

 an increase in size and activity, so that the secretion appears to 

 control or augment growth, particularly that of bone. 



In addition to the above glands there are to be found included in 

 other organs of the body patches of cells with a glandular appear- 

 ance, which presumably produce hormones. Beyond noting the fact 

 that in the case of the reproductive organs the secretions are probably 

 responsible for the development of some of the secondary sexual 

 characters, i.e. characters which are not concerned with the actual 

 production or transmission of the sexual products, but nevertheless 

 differentiate the sexes one from the other, it is not intended to enter 

 into any further details of such glands here. 



We have already seen that the central nervous system 

 takes its place as the great controlling and guiding centre of the 

 animal, but its action is not all powerful, and it is naturally dependent 

 on the body of which it forms a part. The maintenance of the general 

 normal activities of the body and of the fitness of the whole depend 

 to no small extent on hormones secreted by the ductless glands. 



Life History of the Frog. 



Early in the year, about the middle or end of March, the 

 frogs awake from their hibernation and seek water, where they 

 congregate in pairs, and the male, almost silent during the remainder 

 of the year, commences to croak vigorously. Reproduction in the 

 frog is sexual, that is, it involves the union of an ovum produced by 

 an adult female and a spermatozoon, the product of an adult male. 

 The male seeks the female and clasps her tightly round the body 

 with his fore limbs, the callous pad on the first finger having become 

 enlarged and roughened to allow of his doing this easily, and they 

 remain together during the egg laying. As the eggs pass from the 

 oviducts to the cloaca and so to the outside the male pours over 

 them the spermatic fluid containing the spermatozoa, and they are 

 fertilised outside the body of the female. The ovum is a single cell 

 with a nucleus, but is very much enlarged by the inclusion of an 



