ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 507 



hints of ancient structures now pbylotically lost, or has the early incidence 

 of degenerative processes induced a form of structure which never existed 

 at all in adult life ? 



Development of the Hypophysis in Birds.* — Constantin J. Economo 

 finds that the endoderrn has nothing to do with the formation of the 

 hypophysis in birds. The processus infundibuli arises as an outgrowth 

 of the floor of the tweenbrain, and is the equivalent of the saccus vascu- 

 losus of fish. The processus forms a distinctly tubular infundibular 

 gland with a duct opening into the ventricle, just as the saccus vasculosus 

 does in fish. From the upper wall of Eathke's pocket, the hypophysial 

 outgrowth arises, and gives off a right and left process much as it does 

 in reptiles. The middle process becomes extensively branched, and 

 constitutes the median and largest part of the hypophysis. The branches 

 are at first solid, but later their club-shaped ends become hollow. The 

 lower part of the process together with the upper region of Rathke's 

 pocket forms the hypophysial duct, by means of which the cavity of the 

 hypophysis comes into communication with the mouth-cavity. At this 

 stage the hypophysis begins to secrete, but the duct is gradually 

 narrowed, and is obliterated in the chick at the 7-10th day. The lateral 

 hypophysial outgrowths do not disappear as in reptiles, but persist until 

 the time of hatching. 



Development of Crocodilus madagascariensis.f — Dr. A. Voeltzkow 

 has been able to make some observations on the little-known early de- 

 velopment of this form, and on the yolk-sac and the development of the 

 blood and blood-vessels. As regards the development of the germ- 

 layers, there is much general resemblance to the conditions found in 

 Podocnemis. In connection with the development of the yolk-sac, the 

 author gives an interesting comparative account of the conditions under 

 which yolk exists in vertebrates, and the organs by means of which it is 

 absorbed. In the crocodile in the earlier stages the yolk-sac epithelium 

 is of great importance in yolk-absorption. It takes up the particles of 

 yolk and conveys them to the blood-system. Later, when yolk-absorp- 

 tion becomes more rapid, a peculiar system of blood-vessels is developed, 

 whose capillaries come into contact with almost every yolk-spherule. 

 In regard to the blood and blood-vessels, the author finds that in its 

 first origin the blood is endodermal, and precedes the formation of 

 blood-vessels. The endothelium of the blood-vessels is mesodermic in 

 origin, and arises without the participation of the blood-cells. The 

 blood at this time increases by the division of its component cells, and 

 not by budding from the walls of the vessels. 



Visceral Clefts of Lacerta.} — Dr. K. Peter describes fifteen stages 

 in the development of the lizard's visceral clefts, and maintains that their 

 origin is wholly endodermic. Neither an aortic arch nor an external 

 groove is necessary for their definition. Every definitely circumscribed 

 lateral diverticulum of the gut, down to the cardiac groove or the sinus 

 cervicalis, which arises by proliferation, may be regarded as the pri- 

 mordium of an oesophageal pouch. On this view the lizard has six, and 

 five of these always come into contact with the epidermis. 



* SB. Akad. Wias. Wien, cviii. (1899) pp. 281-97 (4 pis.). 



t Abh. Senckenberg. Nat. Ges., xxvi. (1901) pp. 339-418 (7 pis. and 5 figs.). 



j Arch. Mikr. Anat., Mi. (1901) pp. 705-65 (3 pis. and 2 figs.). 



