146 BRAIN AND BODY OF FISH 



in \\ liicli there is very marked enlargement and a great increase of 

 eosinophil cells. Newton in Evans's Advances in Physiology says, 

 " In spite of the presence of only three types of cell in the anterior 

 pituitary it is nevertheless the birthplace of a number of hormones. 

 These act on the general bodily growth, the gonads, the mammary 

 glands, the thyroid and carbohydrate metabolism, and other tissues 

 and glands." What is of interest to us in the study of the eel is 

 obviously not the mammary glands. But bodily growth, the gonads, 

 the thyroid, and general metabolism all enter into the picture of 

 the complicated functions of the anterior pituitary. The earliest 

 knowledge of the functions of the pituitary were connected with 

 growth in certain pathological conditions. In mammals the anterior 

 lobe secretes a growth hormone which jDroduces, if in excess, gigan- 

 tism in children, and in adults acromegaly. 



The relationship between the gonads and the anterior pituitary 

 is based on accurate observation. The secretions of the ovary 

 are dependent on the pituitary and occur in a cyclic fashion. These 

 fimctions of the gonads are not automatic, for removal of the 

 pituitary in immature animals prevents their apj^earance, and in 

 mature animals leads to their arrest. Implantation of anterior 

 pituitary substance, or the injection of suitable extracts before 

 puberty, causes precocious sexual matm-ity. It is not surprising, 

 therefore, to find in the eel about to migrate a great enlargement of 

 the anterior pituitary. It has already been stated that the source 

 of the gonadotropic hormones is in doubt, but the anterior pituitarj- 

 is increased in nearly all species during jDregnancy. This, in 

 mammals, is said to be due to chromophobe cells, but in man 

 some eosinojihile cells are produced and are kno^vn as pregnancy 

 cells. It is clear that so far as my observations are concerned, 

 Avhich extend over a period of over tw^o years, that the enlargement 

 of the anterior pituitary in the eel is due to a gi'eat increase of 

 acido|)hile cells. It is interesting to refer to some earher work on 

 the stimulus for a breeding migration, especially in the eel. 



Walter Heape suggested that the immediate stimulus came 

 from the periodic increase of the internal secretions, elaborated by 

 the gonads. John Hammond (1925) explains his observations on 

 growth and reproduction, by assuming that the anterior pituitary 

 hormone is responsible at different times for stimulating both 

 processes, its physiological effect being transferred from one function 

 to the other in the j^rocess of individual fife. Heape w^as very 

 definite in his view that the imimlsc to migrate is induced by changes 

 in the functional activity of certain organs included in the re- 

 jM'oductive system, and suggests " that the details of the problem 



