ZOOLOGY A>'D BOTANY, MICEOSCOPY, ETC. 367 



origin ; (2) germ-cells of retro-peritoneal origin ; and (3) germ-cells of 

 endoderm (yolk-sac) origin. The germ-cells derived from the yolk- 

 sac may possibly all be laid during the first spawning. Through the 

 peritoneum the mesoderm supplies by far the greatest number of 

 germ-cells. The peritoneal cell always remains in a sufficiently 

 undifferentiated state to metamorphose, if needed, into a germ-cell. 

 The changes undergone in the differentiation of an oogonium into an 

 oocyte are more important and extensive, as far as the nucleus is 

 concerned, than those of the peritoneal cell when becoming a germ-cell. 

 There is no continuity of germ-cells in frogs and toads at least. 



Intra-uterine Eggs of Heterodontus (Cestracion) philippi.* — 

 W. A. Haswell describes the segmentation observed in uterine eggs of 

 this shark. The lines of cleavage are confined to the area of the 

 "orange-spot." A sub-elliptical blastoderm presents the appearance on 

 a surface view of an irregular ring of larger cells separated from one 

 another by fissures having a radial arrangement, and surrounding an 

 area of smaller cells of great irregularity in size and shape. A later 

 stage shows a segmentation cavity beneath the blastoderm. Later on, 

 the segmentation cavity has become a large space below the posterior 

 end of the blastoderm, with a thin roof through which the cavity shows 

 itself as a dark area in the Hving egg. In regard to the red colouring 

 matter which produces the "orange-spot" in Elasmobranchs, it is 

 suggested that it may play the part of a respiratory pigment aiding in 

 the oxidation of the massive blastoderm and the underlying parablast. 



Infection of Hens' Eggs.t— Philip B. Hadley and Dorothy ^V. 

 Caldwell found out of 2520 fresh eggs that 8-7 p.c. showed bacterial 

 infection in the yolk. N^one of the 111 whites examined showed 

 infection, and the yolks of the same eggs gave a percentage slightly 

 less (4-5) than the average of this series (7-7). The percentage of 

 infection obtained for individnal hens per year varied between 2 • 8 and 

 15, the average being 9. No hen laid exclusively sterile eggs during 

 any full year. No correlation was observed between percentage of 

 infection and " hatchability," nor between percentage of infection and 

 fecundity, age of the birds, or the season of the year. The percentage 

 of infection for unfertile and for fertilized eggs was essentially the same. 

 The bacterial types from one series consisted of eleven cocci, twenty- 

 eight rods and one spirillum. 



The most probable source of primary infection is in the ovaries of 

 the fowl, which become infected by bacteria escaping from the intestine 

 into the portal circulation. Tlie primary infection plays no role in 

 bringing about the decomposition of eggs. For the factors determining 

 decomposition secondary infections must be looked to. The nature 

 and extent of the ordinary primary infection stands in no causal relation 

 to embryo-mortality in incubating eggs, and losses in " dead-in-sheM " 

 embryos cannot be explained on these grounds. 



* Quart. Journ. Micr. Sci., Ixi. (1916) pp. 313-6 (2 figs.). 



t Agric. Exper. Stat. Rhode Island, Bull. No. 164 (1916) p. 1-70. 



