ZOOLOGY AND BOTANY, MIOKOSCOPY, ETC. 213 



which it is partially imbedded ; in the next stage certain of the cells 

 forming the upper wall of the neurenteric canal become aggregated 

 together and form the chorda layer ; the median cell process into which 

 the walls of the neurenteric canal are prolonged in front gives off a row 

 of cells which are free anteriorly but posteriorly connected with the 

 canal walls ; immediately in front of the lower aperture of the canal 

 the median cell process becomes greatly widened, further forward it 

 becomes narrower ; posteriorly this layer of cells passes, gradually 

 narrowing without any break, into the chorda layer. The mesoderm 

 appears as a plate on either side near the chorda layer, and anteriorly 

 is in contact with it, posteriorly it diverges from the middle line and 

 is not in contact with the chorda layer ; in a later stage the chorda has 

 become formed throughout the whole embryonal layer ; anteriorly it 

 appears as a thickening of the endoderm without coming into contact 

 with the free-lying plate of mesoderm which is placed between the 

 endoderm and ectoderm ; further back the chorda is attached laterally 

 to the mesoderm while the endoderm lies beneath it and gets farther 

 and farther separated from it. 



In the concluding section of the paper the author discusses a 

 number of points which arise out of the facts detailed, and criticises 

 Hertwig's views on the chorda and the formation of the mesoderm as 

 well as the observations of Kupffer and Weldon. 



Spindle-shaped Bodies in the Yolk of Young Ova of Frogs.* — 

 O. Hertwig, after a reference to the discoveries by Fol, Schafer, and 

 Balbiani, of nuclei in the ova of various animals, describes those 

 which he himself has detected in the yolk of frogs' eggs. The spindles 

 are peculiar in form ; thickest in the middle. They pass out into 

 long, thin, and fine points ; they are never quite straight, and are 

 ordinarily coiled in an S-shape. When present, they are always but 

 few in number, three are rare, two are sometimes and one generally 

 found. All possible intermediate stages may be seen between these 

 and others which are much smaller ; the latter are sometimes found 

 in company with the former, or alone, when a larger number is always 

 present. 



The spindle-shaped bodies were always absent from very small 

 ova ; but in their place it was observed that several oval or spherical 

 bodies were found lying near the germinal vesicle ; they consist of 

 a hyaline substance, which gives, with osmic acid, much the same 

 reactions as the germinal spots and the spindle-shaped bodies. While 

 the above description applies to what is seen in the ova of Mana 

 temporaria, a general though not exact agreement obtains in the case 

 of B. esculenta. The author is of opinion that further investigations 

 are required before we can certainly say whether the structures he 

 describes are true nuclei, or peculiar concretions. 



Development of the Rays of Osseous Fishes. f— The main con- 

 clusion at which J. A. Eyder arrives is, that it is the mesoblast 

 which is involved in giving origin to the fibrous embryonic rays, and 



* Morphol. Jahrb., x. (1884) pp. 337-43 (1 pi.). 

 t Amer. Natural., xix, (1885) pp. 200-4 (5 figs.). 



