20 



THE MICROSCOPE AND ITS REVELATIONS. 



accepted by Haeckel, whose representation of a living specimen of Bathy- 

 bius, with imbedded coccoliths, is given in Fig. 293, 4. The observations 

 made in the ' Challenger' Expedition, however, have not confirmed this 

 view; the supposed BathyMus being a gelatinous precipitate, consisting of 

 sulphate of lime, slowly deposited in water to which strong spirit has 

 been added. Whatever be their nature, Coccoliths and Coccospheres are 

 bodies of great interest; since their occurrence in Chalk and in very early 

 Limestones ( 699) is an additional link in the evidence of the similarity 

 of the conditions under which they were formed, to those at present pre- 

 vailing on the sea-bed of the Atlantic and others oceans. Two distinct 

 types are recognizable among the Coccoliths, which Prof. Huxley has 

 designated respectively discoliths and cyatholiths. The former are round or 

 oval disks, having a thick strongly-refracting rim and a thinner internal 

 portion, the greater part of which is occupied by a slightly-opaque, cloud- 

 like patch lying round a central corpuscle (Fig. 293, 5). In general, the 

 ' discoliths ' are slightly convex on one side, slightly concave on the other, 

 and the rim is raised into a prominent ridge on the more convex side; 



FIG. 293. 



Coccoliths and Coccospheres: 1, 2, 7, Cyatholiths seen obliquely; 3, Coceosphere, with im- 

 bedded cyatholiths; 4, Coccoliths imbedded in supposed protoplasmic expansion ; 5, Discolith 

 seem in front view; -6, Cyatholith seem in front view, showing' (1) central corpuscle, (-2) granular 

 zone, (3) transparent outer zone; 8, 9, Discoliths seen edgeways. 



so that when viewed edgewise, they present the appearances shown in figs. 

 8, 9. Their length is ordinarily between l-4000th and l-50QOth of an 

 inch; but it ranges from l-2700th to 1-11, 000th. The largest are com- 

 monly free; but the smallest are generally found imbedded among heaps of 

 granular particles, of which some are probably discoliths in an early stage 

 of development. The ' cyatholiths, ' also, when full grown, have an oval 

 contour ; though they are often circular when immature. They are convex 

 on one face and flat or concave on the other; and when left to themselves, 

 they lie on one or other of these two faces. In either of these aspects, they 

 seem to be composed of two concentric zones (fig. 6, 2, 3) surrounding 

 an oval thick-wall central corpuscle (1), in the centre of which is a clear 

 space sometimes divided into two. The zone (2) immediately surround- 

 ing the central corpuscle is usually more or less distinctly granular, and 

 sometimes has an almost bead-like margin. The narrower outer zone (3) 



