THE CENTROSOME 



51 



some other reagents, and surrounded by a cytoplasmic radiating aster 

 or by a rounded mass known as the a t traction-spJicr c (Figs. 8, 49, etc.). 

 As a rule it lies in the cytoplasm, not far from the nucleus, and 

 usually opposite an indentation or bay in the latter ; but in a few 

 cases it lies inside the nucleus (Fig. 148). In epithelia the centro- 

 sonies (usually double) lie as a rule near the free end of the cell 

 (Fig. 23).i 



There is still much confusion regarding the relation of the centro- 

 some to the surrounding structures, and this has involved a corre- 

 sponding ambiguity in the terminology. We will therefore only 

 consider it briefly at this point, deferring a more critical account to 

 Chapter VI. In its simplest form it is a single minute granule, which 

 may, however, become double or triple (leucocytes, connective tissue- 

 cells, some epithelial cells) or even multiple, as in certain giant-cells 

 (Fig. 14, D), and as also occurs in some forms of cell-division (Fig. 

 52). In some cases (Figs. 8, C, 120, 148) the " centrosome " is a 

 larger body containing one or more central granules or " centrioles " 

 (Boveri); but it is probable that in some of these cases the central 

 granule is itself the true centrosome, and the surrounding body is part 

 of the attra( tion-sphere. During the formation of the spermatozoon 

 the centrosome undergoes some remarkable morphological changes 

 (p. 171), and is closely involved in the formation of the contractile 

 structures of the tail. 



The nature and functions of the centrosome have formed the sub- 

 ject of some of the most persistent and searching investigations of 

 recent cytology. Van Beneden, followed by Boveri and many later 

 workers, regarded the centrosome as a distinct and persistent cell- 

 organ, which like the nucleus was handed on by division from one 

 cell-generation to another. Physiologically it was regarded as being , 

 the especial organ of cell-division, and in this sense as the " dy- 

 namic centre" of the cell. In Boveri's beautiful development of this 



the following year, in dycyemids. The name is due to Boveri ('88, 2, p. 68). Van Beneden's 

 and Boveri's independent identification of centrosome in Ascaris as a permanent cell-organ 

 ('87) was quickly supported by numerous observations on other animals and on plants. In 

 rapid succession the centrosome and attraction-sphere were found to be present in pig- 

 ment-cells of fishes (Solger, '89, '90), in the spermatocytes of Amphibia (Hermann, '90), in 

 the leucocytes, endothelial cells, connective tissue-cells, and lung-epithelium of salamanders 

 (Flemming, '91), in various plant-cells (Guignard, "91), inthe one-celled diatoms (F.utschli, 

 '91), in the giant-cells and other cells of Ixuie-marrow (Heidenhain, Van Bambeke, Van der 

 Stricht, '91), in the flagellate Noctiluca (Ishikawa, '91), in the cells of marine algae (Stras- 

 burgcr, '92J, in cartilage-cells (Van der Stricht, '92), in cells of cancerous growths (epitheli- 

 oma, Lustig and Caleotti, '92), in the young germ-cells as already described, in gland-cells 

 (Vom Rath, '95), in nerve-cells (Lenhossek, '951, in smooth muscle-fibres (Lenhossek, '99), 

 and in embryonic cells of many kinds (Heidenhain, '97). Many others have confirmed 

 and extended this list. Guignard's identification of the centrosomes in higher plants is 

 open tu grave doubt {^cf. p. 82). ^ Cf. p. 57. 



