1888.] MICKOSCOPICAL JOURNAL. 149 



Usually the microsomata are grouped together into one or more masses which 

 appear as little rounded bodies. These are what have long been known 

 under the name of nucleoli. Of course if the microsomata are the funda- 

 mental life elements the nucleoli must be regarded as special centres of ac- 

 tivity. And this is not the end. It frequently happens that inside of the 

 nucleolus there is a still smaller body, and sometimes inside of this still an- 

 other. Each of these masses of microsomata may be looked upon as succes- 

 sively nearer the real centre of activity of the cell. Cytologists are indeed 

 now inclined to think that a single one of these minute microsomata is enough 

 to be the starting-point of a cell ; and if this is true the complexity of a single 

 cell or a single nucleus or even a single nucleolus, is almost inconceivably 

 great. Perhaps the best evidence of this is shown by the phenomena of 

 karyokinesis. Every student of biology knows of the great changes taking 

 place in a cell dui^ing cell division. These complicated karyokinetic figures 

 are formed in the nucleus by the movements of the microsomata and the pro- 

 toplasmic filaments. No two cells are known to go through exactly the same 

 phases during cell division, which is sure enough proof that the nucleus is 

 not a simple body, but one of extreme complexity. 



In short, the study of the last few yearns has developed a new branch of 

 science. The study of cytology is fast coming to have its special students, 

 its special literature, and its special terminology. Cytology includes not 

 only the study of the external appearance of cells, but even more the study 

 of their internal structure, and the structiu'e of protoplasm. vSome day it is 

 not improbable that it may include a study of the history in the early pro- 

 cesses in the formation of cells from the simpler elements of life, just as em- 

 bryology includes the study of the history of the development of animals. 



Wksleyan University, Miudlbton, Ct., July 14,1888. 



Three cruises of U. S. S. Blake in the Gulf of Mexico, Caribbean Sea, 

 and along the Atlantic Coast of the United States.* 



By Prof. ALEXANDER AGASSIZ. 



These two volumes form volumes xiv and xv of the Bulletins of the 

 Museum of Comparative Zoology, at Cambridge, Mass. While scientific 

 in character, they are not exhaustive monographs, but a narrative of the cruises, 

 and they attempt to picture for the reader the topography and inhabitants of 

 the sea, both its surface and its depths, a ' contribution to North American 

 Thallasography.' 



Passing over 38 pages devoted to the interesting account of the apparatus, 

 we find chapter iii (^41 pages) devoted to the Florida reefs, separated from 

 the islands or keys by a channel of from 3-15 niiles in width, navigable for 

 small vessels. The coral island theories are reviewed in connection with 

 these reefs, and Darwin's theory, explaining the growth of atolls as solely 

 due to the subsidence of volcanic peaks, is objected to. ' We must look to 

 many other causes than those of elevation and subsidence for a satisfactory 

 explanation of coral-reef formation. All important among these causes are 

 the prevailing winds and currents, the latter charged with sediment which 

 helps to build extensive plateau from lower depths to levels at which corals 

 can prosper.' 



The chapter on pelagic fauna and flora is full of intei'est for the biological 

 student. Including representatives of nearly all littoral forms, they are usually 

 smaller, translucent, and often of most exquisite color, tinting the surface 

 for miles, so numerous are they, and at night so brilliantly phosphores- 



*2 vols., pp. 314 ; pp.220. Boston. Houghton, MifHin & Co., 1888. 



