EEPORT ON THE GENUS ORBITOLITES. 35 



The cylindrical chamberlets of tlie intermediate stratum, as seen in vertical section 

 (PI. VI. fig. 9,c,c), generally pass in a nearly straight, parallel and separate course 

 through its whole thickness; but this is by no means constantly the case. For not only 

 are there occasional communications between the adjacent chamberlets of the same row, but 

 sometimes a chamberlet, after extending through only a part of the thickness of the disk, will 

 merge, as it were, in the two chamberlets on either side of it, which, when no longer kept 

 apart, incline towards one another, as shown externally in the direction of the rows of 

 marginal pores (fig. 4, d"). The same departure from strict regularity is shown in the col- 

 umnar sub-segments of the sarcodic body (PL V. fig. 14, d, e) ; adjacent columns of the 

 same annulus inosculating not unfrequently with one another. But all the columns of 

 any one annulus terminate above and below in the two annular stolons (h, h)' of 

 their own annulus, which thus unite them into one continuous system. 



By these varied methods every part of the labyrinthic cavitary system of this most 

 complex ty[3e of Orbitoline structure is brought into free communication with every other 

 part ; so that a circulation of the protoplasmic body-substance may be constantly 

 maintained, which shall difi'use through the whole of it whatever nutrient material is 

 drawn in through the marginal pores, and also get rid. through those j)ores, of any efiete 

 matter which is unfit to be kept in the organism. Notwithstanding the extent to 

 which structural specialisation is here carried in the shelly disk — as manifested in the 

 separation of the superficial layers from the intermediate stratum — I have not been able 

 to trace any indication whatever of a corresponding functional specialisation. There is 

 not, so far as I have been able to make out, any differentiation of parts throughout the 

 entire sarcodic body, every portion of it presenting the same aspect, and possessing the 

 same attributes, as the rest. This homogeneousness is further manifested in two ways : — 

 first, by the production, from any part of the disk, of outgrowths which present, under 

 strangely irregular forms, its characteristic peculiarities of internal structure ; and second, 

 by the completeness with which injuries of any part of the disk are repaired, its cyclical 

 plan of growth being renewed, and its discoidal form more or less perfectly restored. 



Irregularities. — The tendency to form irregular outgrowths shows itself especially in 

 the large and massive specimens, which, as already stated, were found living in the rock- 

 pools on the summit of the Fiji reef ; and may be taken to indicate an exuberance of 

 formative power, that probably depends upon the higher temperature and greater 

 abundance of food which the animals there enjoy. In PL VIL is given a series of 

 portraits of such disks, all drawn to the same scale of four diameters ; a full-sized disk of 

 regular form being represented for comparison in fig. 3. The disk portrayed in fig. 1 

 exhibits an incipient " crumpling " of the marginal annuli, which shows their peripheral 

 extension to have been more rapid than their radial, so that these annuli are thrown into 

 irregular folds ; whilst a small vertical outgrowth, having the character of a perfect half- 

 disk, but very thick in proportion to its diameter, arises from the central portion, probably 



