362 SUMMARY OF CURRENT RESEARCHES RELATING TO 



If transferred outside the vessels, the erythroblastic tissue, as seen in the 

 allantois of the chick and in the kidney of the mammal, continues its 

 proliferation and its homoplastic differentiation. The extravascular 

 erythropoiesis in mammals, until new evidence is at hand, may be looked 

 upon as the development of specific blood-cells, which can no longer 

 alter their metabolism in response to environmental factors, J. A. T. 



So-called Thymus IV. of Cat.— Fred. W. Stewart (Amer. Journ 

 Anat, 1918, 24, 191-223, 4 pis.). The ultimobranchial body of the 

 cat develops essentially as a fifth pharyngeal pouch, although as such it 

 does not make ectodermal contact. The internal thymic lobule of the 

 thymus (the so-called Thymus IV.) is not a branchiomeric structure. It 

 is contributed to by the whole of the ultimobranchial body, or by all 

 that does not degenerate. The ultimobranchial body of the cat is an 

 essentially regressive structure. J. A. T. 



Development of Hypophysis of Rabbit.— Wayne J. Atwell 

 {Amer. Journ. Anat., 1918, 24, 271-337, 39 figs.). The hypophysis 

 eyagination is plainly visible in a rabbit embryo having sixteen primi- 

 tive segments, on the earlier part of the tenth day after insemination. 

 The endoderm does not contribute. The stalk connecting the hypo- 

 physis with the oral epithelium becomes solid during the fourteenth day ; 

 it loses its connexion with the epithelium at a variable time between the 

 sixteenth and twenty-fourth day. The residual lumen of Ratke's pouch 

 at first extends from end to end of the epithelial portion ; later it 

 does not reach to the nasal extremity. From the thickened epithe- 

 lium just nasal to the early Ratke's pockets two ridge-like elevations 

 are developed ; these are the " lateral lobes," the primordia of the 

 pars tuberalis and of a temporary cortical plate at the nasal extremity of 

 the gland. Their development is followed in detail. The neural lobe 

 undergoes a series of complex foldings and compressions which result 

 in the dividing up and partial obliteration of the cavity of the lobe, 

 and in the formation of a medullary layer and a cortical layer. It 

 seems that processes grow from the neural lobe into the mtermediate 

 part. The lateral lobes of mammals and reptiles seem to be homologous, 

 but it is precarious to say the same of the lateral lobes of Elasmobranchs, 



J. A, T. 



Development of Hypophysis of Anura.— W. J. Atwell {Anat. 

 Record, 1918, 15, 73-92, 18 figs.). There are three epithelial lobes and 

 a neural lobe. The lobes of epithelial origin are the anterior lobe proper, 

 the pars intermedia, and the pars tuberalis. From their development 

 and their mature structure these lobes in Anura may be considered 

 homologous with corresponding lobes in all higher vertebrates. The 

 anterior lobe proper develops from the main central portion of the 

 solid epithelial primordium. It comes to be caudal and ventral to the 

 other portions. The pars intermedia develops from the caudal tip of 

 the hypophysial primordium. The pars tuberalis has a paired origin 

 in the lateral lobes, which appear very early and become detached from 

 the brain-floor in the pia mater. J. A. T. 



