250 H. E. JORDAN 



no larger than in dogs, renders it very improbable that it is an 

 indispensable or even serviceable organ for mammals. Moreover, 

 the further observation that it frequently becomes cystic with- 

 out producing noticeable morbid effects increases the improb- 

 ability. Thus in two out of eleven cats examined it consisted 

 simply of a pedunculated vesicle with thin fibro-cellular wall. 

 Its vestigial and variable character in the opossum (Jordan, '11) 

 supplies additional support to the opinion that the pineal body is 

 a rudimentary organ functionally nil. The recent work of Exner 

 and Boese ('10) •with rabbits is also in accord with this position. 

 These investigators removed the epiphyses of ninety-five young 

 rabbits but were unable to detect any effect on growth or the 

 appearance of sexual maturity among the six that survived. 

 However, in man the pineal body acquires considerable size (ca. 

 7 mm. x 5 mm.) and exhibits glandular characteristics, suggest- 

 ing the function of elaborating an internal secretion. Moreover, 

 it frequently becomes the seat of neoplasms whose presence 

 involves certain symptoms which cannot be accounted for on the 

 basis simply of pressure on adjacent structures (Lord, '99; Exner 

 and Boese, '10; and Pappenheimer, '10). 



When it was discovered that the sheep's pineal body was of 

 considerable size (ca. 5 mm. x 3 mm. to 8 mm. x 5 mm.) the inves- 

 tigation was restricted to an intensive study of the * gland' in this 

 form. This seemed the wiser since quantities of material could be 

 obtained for experimentation and preservation in perfectly fresh 

 condition. The large size and the constancy of size (commonly 

 about 7 mm. x 5 mm.; more than fifty bodies were examined) 

 and form, indicated that here, if anj^where, the body should have 

 physiologic significance. Accordingly, the effects of aqueous 

 extracts on various animals were studied, — with the result already 

 recorded (i.e., fall in blood pressure and transient diuresis — Eyster 

 and Jordan, '11). A further step involves the extirpation of the 

 body in the sheep, a work now in progress but as yet without 

 results. 



Still another step in the complete study contemplated, was to 

 trace the developmental history of this structure. The present 

 paper is an attempt to record this history from about the second 



