FOKAMINIPBRA — ORBITOLITB. 



441 



Fig. 206. 



Simple disk ot OrHtolites cffinplaTiatus, laid open to 

 show its interior structure -.—a, central cell ; 6, circum- 

 ambient cell surrounded by concentric zones of cells, 

 connected with each other by annular and radiating 

 passages. 



cient to rub down one of the surfaces upon a stone, and then to 

 mount the specimen in balsam. Each of the supei-ficial eleva- 

 tions will then be found 

 to be the roof or cover 

 of an ovate cavity or cell, 

 which communicates by 

 means of a lateral passage 

 with the cavity on either 

 side of it in the same 

 ring; so that each circu- 

 lar zone of cells might be 

 described as a continuous 

 annular passage, dilated 

 into cavities at intervals. 

 On the other hand, each 

 zone communicates with 

 the zones that are inter- 

 nal and external to it, by 

 means of passages in a 

 radiating direction; and 

 it is curious that these passages run, not from the cells of 

 the inner zone to those of the outer; but from the connect- 

 ing passages of the former to the cells of the latter; so that 

 the cells of each zone alternate in position with those of the 

 zones that are internal and external to it. The radial passages 

 from the outermost annulus make their way at once to the mar- 

 gin, where they terminate, forming the "pores" which (as al- 

 ready mentioned) are to be seen on its exterior. The central 

 nucleus, when rendered sufficiently transparent by the means 

 just adverted to, is found to consist of a central cell (a), usually 

 somewhat pear-shaped, that communicates by a narrow passage 

 with a much larger circumambient cell (b), which nearly sur- 

 rounds it, and which sends oft" a variable number of radiating 

 passages towards the cells of the first zone, which forms a com- 

 plete ring around the nucleus.' 



288. The idea of the nature of the living occupant of these 

 cavities, which might be suggested by the foregoing account of 

 their arrangement, is fully borne out hj the results of the exami- 

 nation of the sarcode body, that may be obtained by the macera- 

 tion in dilute acid (so as to remove the shelly investment) of 

 specimens of OrbitoUte, that have been gathered fresh from the 

 sea- weeds to which in the living state they are found adherent, 

 and have been kept in spirit. For this body is found to be com- 

 posed (Fig. 207) of a multitude of segments of "sarcode," pre- 



' Although the above may be considered the typical form of the Orbitolite, yet, in a 

 very large proportion of specimens, the first few zones are not complete circles, the 

 early growth having taken place rather in a spiral than in a radial direction; between 

 these two plans, there is every variety of gradation ; and even M'here the spiral is most 

 distinctly marked in the first instance, the additions soon come to be made in concentric 

 zones. 



