256 Journal of Applied Microscopy. 



having eggs with large quantities of yolk, birds for example. This comparison 

 is perfectly justifiable. In amphibians the blood islet, with that portion of hypo- 

 blastic yolk which it occupies, is comparable to the area vasculosa of vertebrates 

 with meroblastic eggs. 



The analogies between the two are numerous. In all vertebrates in which 

 the vascular area exists, it is the center of the first formation of blood. In the 

 amphibian, the blood islet, occupying the individal surface of the hypoblastic 

 yolk, is not only the first but the exclusive place of blood formation. 



Another comparison, yet more interesting, is that in the Amphibia, as in the 

 vertebrates having the area vascula, the vascular system at large and the blood in 

 the blood islet form independently of the heart and chief embryonic vessels and 

 at first have no connection with the former structures. Secondarily, this connec- 

 tion is established. 



Yet another point is that the midcentral blood islet and the part of the vitel- 

 lin veins forming from it appears to be of value as an extra embryonic vascular 

 system comparable with the vascular yolk apparatus of reptiles and birds. It is 

 comparatively easy to explain the primitive independence of the vascular area 

 and the body vessels of the embryo in vertebrates having the embryo lying spread 

 out over a very abundant nutritive yolk, but in the amphibians, where the quantity 

 of nutritive yolk is not only less in amount, but also distributed in all cells form- 

 ing the embryonic arc, this arrangement is less comprehensible. 



Many other points of great interest and great value are brought out by the 

 author. Questions now open in embryology about this most difficult and vexed 

 question are discussed, and the paper is one of great value to those interested in 

 this subject. a. m. c. 



Nemec, Dr. B. Centrosome and Nucleus. The author compares the cell divisions 

 Anat. Anzeier. 14: i8q8, pp. 560-^80. • 1 • 1 1 r • 



m which the centrosome functions with 



those in which it seems to be absent, as in higher plants. No doubt exists as to 

 the essential resemblance, and the author shows that in a cell without a centro- 

 some the nucleus serves the same purpose in the prophases and the anaphases. 

 The centrosome is really, in such cells, homodynamous with the nucleus before 

 and after nuclear division. a. m. c. 



Arnold, Prof. J. The Structure of Cytoplasm. Prof. Arnold examined many kinds of 

 Arch. fr. Mikr. Anat. 52: 1808, pp. n4-ii;i. n • r 1 



cells in reference to the structure of 



their substance. In many cases, as in leucocytes and bone marrow, the plasma- 

 somes are present and are bound by thread-like or rod-like processes into systems, 

 sometimes reticular, sometimes spongy. The plasmasomes enclose granules 

 (somatia) variously disposed, and a hyaline substance (paraplasm) in the inter- 

 stices of the system. A great variety is possible in the structure of these systems 

 with these materials. 



In nervous tissue Arnold describes a general occurrence of rows of granules. 

 In ganglion cells at least two different substances forming systems of granules are 

 set apart from the hyaline interstitial substance. It may be that the one system 

 composed of neurosomes has to do with conduction, while the other composed of 

 plasmasomes has to do with nutrition. a. m. c. 



