ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 345 



valent to two epithelial layers, will have no weight for those who 

 remember that in the Chfetognatha the mesoblast appears, is lost, and 

 again appears ; that in Bony Fishes the nerve-cord is at first solid ; or 

 the mode of development of various sensory and glandular organs. 

 Hertwig concludes by entering into a detailed criticism of the remarks 

 of His on the " coelom-theory " of his brother and himself. 



I'he earlier part of the paper is occupied with the Amphibia — 

 where Bana temporaria is taken as the type ; in dealing with meso- 

 blastic ova (Elasmobranchs, reptiles, birds, and mammals) the 

 author confines himself to discussing the observations of his fellow- 

 workers, and drawing from them lessons which bear on his general 

 conclusions. 



Inversion of Blastodermic Layers in Rat and Mouse.* — A. Fraser 

 finds that in the common grey rat and the house-mouse we find the 

 same arrangement of blastodermic layers as in the guinea-pig. The 

 decidua appears to differ in the mode of its formation from that which 

 ordinarily obtains, and the very early, rapid, and voluminous forma- 

 tion of its solid mass appears to have some close and constant relation 

 to the peculiar inversion of the blastodermic layers which is found in 

 these rodents. 



Spermatozoon of the Newt.f — Mr. G. F. Dowdeswell describes a 

 minute barb at the extreme point of the " head " of the spermatozoon 

 of the newt, which has hitherto escaped notice. It is 2 /a long and 

 1*5 /x, broad. A similar structure was not found in other sperma- 

 tozoa. It is suggested that the function of the barb is to attach the 

 spermatozoon, and enable it to penetrate into the ovum in the early 

 stages of fertilization, as has been shown to occur by Fol and others. 



Development of the Red Blood-corpuscles. | — W. Feuerstack 

 finds that nucleated red blood-corpuscles arise from colourless blood- 

 cells ; the forms most closely allied to them are the ordinarily spherical 

 coloured cells with an often disproportionately large nucleus — the so- 

 called heematoblasts. Among these we meet with forms which present 

 us with a series of intermediate stages between the ordinary red blood- 

 corpuscle and the typical smaller heematoblasts with a proportionately 

 large peripheral nucleus. The hsematoblasts are derived directly 

 from the colourless cells, in which the nucleus is much smaller. In 

 Amphibia (e. g. Triton) and, to a less degree, in fishes, the formation 

 of the red blood-corpuscle is not so regular as in birds, and we find 

 therefore in them a much greater variety in the size of the hsemato- 

 blasts. 



The answer to the question where this blood-formation goes 

 on is based on the supposition that we must look for it at such 

 points as those in which we find the largest number and youngest 

 stages of forms intermediate between coloured and colourless cells. 

 In the pigeon these points are the osseous medulla, the spleen, the 

 portal system, and the medulla of the young quills of the feathers. 



* Proc. Eov. Soc, xxxiv. (1883) pp. 430-7. 



t Quart. Journ. Micr. Sci., xxiii. (1883) pp. 336-9 (1 fig.). 



i Zeitschr. f. Wiss. ZooL, xxxviii. (1883) pp. 136-64. 



