ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 437 



skeletons. The form of the spicule may depend simply on its chemical 

 nature ; or the inorganic solid material may be laid down in conformity 

 with the shapes of the cells and tissues ; or there may be intermediate 

 cases where the molecular forces play their part in conjunction with, and 

 under the restraint of, the other forces inherent in the system. 



Other chapters deal with the widespread occurrence of the logarithmic 

 spiral, with shapes of shells and eggs, with adaptations of minute archi- 

 tecture, as in bone, to mechanical efficiency, and with the passage from 

 one shape to another as the result of a simple harmonious deformation. 

 The author has shown what promise there is in -the endeavour to carry 

 into the study of organisms the laws and lessons of the inorganic. 



Development of Hypophysis and Related Structures in Mar- 

 supials.* — Katherine M. Parker finds in Bettongia, Macropus, Ferameles, 

 and Trichosurus a pair of head-cavities whose early relations and sub- 

 sequent history show them to be premandibular somites. In Ferameles 

 these structures arise from a prechordal plate which represents a deriva- 

 tive of the antero-dorsal wall of the fore-gut. A well-developed Seessel's 

 pocket or pre-oral gut occurs in some Marsupials ; in Phascolarctos 

 cinereus and Phascolomys mitchelli it forms a constituent part of the 

 liypophysis. 



The primitive relation of the tip of the notochord is one of con- 

 tinuity with the protochordal plate, and in Ferameles continuity is 

 retained between the chorda and the derivatives of the protochordal plate 

 (prechordal plate and Seessel's pocket). As a secondary condition, con- 

 tinuity may be established between the chorda and the hypophysis. 



The development of Ratke's pouch is due to rapid growth of the 

 differentiated epithelium of the hypophysial angle, and not to any 

 mechanical power exercised by the chorda or any other structure. 

 From Katke's pouch in Marsupials there arises a proximal lobe, at the 

 point of junction of the duct with the body of the pouch. This forms 

 the pars tuberalis of the adult pituitary body. 



The glandular structure of the pars distalis (anterior lobe) of the 

 adult is produced either by outgrowth of processes from the walls of 

 Ratke's pouch or by ingrowth of connective tissue into the thickened 

 walls of that structure. Two types of cells, " chromophilic " and 

 " chromophobic," are differentiated in situ in the pars buccalis before 

 the adult condition is fully reached. The pars neuralis arises as a hollow 

 conical outgrowth of the diencephalic floor. It is gradually transformed 

 into a solid, swollen lobe, and is then penetrated by connective tissue. 



Ossification in Ovary.t— Eli Moschcowitz describes three cases of 

 calcification and two cases of ossification in the human ovary. The 

 process in each case involved a corpus albicans. Four stages are re- 

 cognizable : (1) an early discrete multiple deposit within a healed corpus 

 luteum ; (2) a definitely circumscribed deposit of amorphous lime 

 within a corpus albicans ; (3) the formation of primary Haversian 



* Journ. Anat., li. (1917) pp. 181-249 (42 figs.). 



t Johns Hopkins Hospital Bull., xxvii. (1916) pp. 71-8 (4 pis.). 



