ZOOLOGY A..' I) BOTANY, MICROSCOPY, ETC. 635 



in bony fish. Some of their results may be summed up as follows. In 

 many fish {Trutta, Solea, Clupea, Ac.) the primitive lateral plate divides 

 into an internal part forming the intermediary cells, and an external 

 part, the secondary lateral plate, which later divides into the excretory 

 canal and the lateral plate. In Lenciscus and Exoraetus, the primitive 

 .lateral plate divides at once into three parts, the intermediary mass, the 

 excretory canal, and the lateral plate. In regard to the pronephros, the 

 authors believe that their results show that the evidence that it primi- 

 tively existed throughout the segmented region of the trunk in Tele- 

 osteans, is at least as conclusive as that in the case of Amphibians 

 and Cyclostomes. There is a true though rudimentary pronephric 

 chamber, its extent varying in the different species. The aorta, the 

 cardinal veins, the red blood-corpuscles, originate from the intermediary 

 cells, without assistance from hypoblast or sclerotome. The sclerotomes 

 furnish only the axial mesenchyme. 



Development of Lepidosiren paradoxa. * — J. Graham Kerr sum- 

 marises his observations on this subject as follows. The segmentation 

 cavity arises from intercellular chinks, its roof early becomes two- 

 layered, and assumes the character of epiblast. Gastrulation occurs for 

 the most part by a process of true invagination. There is no true 

 opibole, the spreading of small over large cells taking place by delami- 

 nation. Before the segmentation cavity disappears, it is penetrated by 

 a sponge- work of small blastomeres. The rudiments of notochord and 

 mesoderm are at first quite continuous across the middle line, but the 

 notochord remains attached to the hypoblast for some time after the 

 mesoderm has separated off at each side. The mesoderm grows outwards 

 on each side by delamination from the large yolk-cells, and the myoccele 

 arises by the breaking-down of cells in the middle of the myotome. At 

 a later stage, the myotome wall is composed of a single layer of regular 

 columnar cells. The first formed mesenchyme arises from sclerotomic 

 outgrowths, assisted to a slight extent by proliferation from the sub- 

 chordal hypoblast. The solid neural keel arises by thickening of the 

 -deep layer of the epiblast. In its early stages the development of 

 Lepidosiren closely resembles that of Protopterus, and both developments 

 agree very closely with that of the Urodele Amphibians and of 

 Petromyzon, while there is a general resemblance to the conditions seen 

 in Ganoid fishes. The material upon which the research was based was 

 very extensive, and the results emphasise the large amount of variability 

 xvbich exists among embryos of the same stage. 



b. Histology. 



Histology of Functional Mammary Glands.j — Dr. Donate Otto- 

 lenghi finds that the secretion of milk is an active function of the 

 mammary gland-cells, which is not necessarily associated with the 

 degeneration of the cells, though, as a consequence of their great activity, 

 the cells tend to die more or less speedily, according to the individual 

 and the amount of secretion. These dying cells are replaced by the 

 karyokinetic division of the remaining cells, though direct division also 



* Quirt. Journ. Micr. S.-i., xlv. (1901) pp. 1-40 (4 pis. and 4 figs.). 

 f Arch. Mikr. A'iat. lviii. (1901) pp. 5S1-60S (2 pJs.). 



