ZOOLOGY AND BOTANY^ MICROSCOPY, ETC. 367 



given off from tlie secondary nucleus. The primary rays of the polaster 

 have a definite numerical relation to the chromosomata, the number of 

 the latter being twice as large as that of the former. After division 

 the secondary nucleus is formed from the polar elements, that is, the 

 centrosoma and the primary rays, and into it the substance of the 

 spindle-fibres seems again to j)ass. The tip of the head of the sperma- 

 tozoon is formed from the centrosoma. The secondary nucleus formed 

 from the spindle-fibres after the last division of the spermatocytes takes 

 a direct or indirect share in the formation of the covering of the axial 

 filament. The last division of the spermatocytes is of a reducing nature, 

 as it follows directly on the one which precedes it without the inter- 

 calation of a resting-stage ; it corresponds to the division of the second 

 polar globule, and the number of chromatic elements is reduced by one- 

 half. 



Herr Platner concludes with some notes on direct nuclear division 

 in the Malpighian vessels of Insects, which are particularly suitable 

 objects for such investigations. Division was found to be not mere 

 elongation and constriction, but a more complicated process ; this is 

 explained by supposing that there are in the nucleus chromatic elements 

 of different characters ; the more highly differentiated are as nearly as 

 possible divided into two, while those that are less so are more coarsely 

 divided. 



Process of Ossification.* — Dr. Drogoul has investigated the much 

 discussed process of normal ossification in mammals. He emphasizes 

 the observation that the osseous cells do not multiply, but that the 

 reproductive activity is exhibited by the cartilaginous elements, peri- 

 osteal and medullary. His object has been to investigate the cell- 

 divisions in those structures which afford the new tissue. The ossification 

 does not occur in the same way in the epiphysis and in the extremity of 

 the diaphysis; the former is wholly neoplastic, the latter to some 

 extent metaplastic. The articular cartilages are distinguished from the 

 cartilages destined to become ossified in the character and behaviour of 

 their component elements, since only the transitional elements which 

 give rise to the capsule, the ligaments, and the periosteum multiply, 

 never those of the body of the cartilage. The perichondrium is 

 equivalent to the external stratum of the periosteum, and its functions 

 are limited to the protection of the cartilage, in the growth of which it 

 has no share. 



■y. Q-eneral. 



Fresh-water Fauna of Greenland.! — MM. J. de Guerne and 

 J. Eichard report on the result of M. Ch. Eabot's exploration of some 

 fresh-water basins in different parts of Greenland. Two Phyllopods, 

 Brancliinecta paludosa 0. F. Miiller and Lepidurus glacialis Kroyer, 

 previously reported from Greenland, were found abundantly. Cladoeera 

 were represented by twelve species, of which the most widely dis- 

 tributed seemed to be Bosmina arctica. It was interesting to find Holo- 

 pedium gihberum, which is characteristic of the pelagic zone of great 

 mountain lakes, occurring in Greenland in small shallow basins, at the 

 level of the sea. Copepods were represented by Cyclops viridis Fisch., 

 of rare occurrence, and Diaptomus minutus in great abundance. The 



* Atti R. Accad. Sci. Torino, xxiv. (1888-9) pp. 264-8 (1 pi.). 

 t Comptes Eeiidus, cviii. (1889) pp. 630-2. 



