36 



THE VOYAGE OF H.M.S. CHALLENGER. 



from its "nucleus." Similar central outgrowths are by no means uncommon, and 

 sometimes show themselves at an early stage, as in the small disk which is represented 

 in PI. VIII. fig. 1, under a magnifying power of ten diameters. Another curious 

 irregularity in a young disk is shown in PI. VIII. fig. 3. Whether from accident or 

 from some obstruction to the growth of the disk on its left side, the peripheral additions 

 do not pass completely round the central portion, and the thick vertical crest seems to 

 represent a fold of the peripheral annuli produced by the exuberance of their material. 

 Another small specimen represented under the same power in PL VIII. fig. 11, has a very 

 curious " twin" disk, which must have either begun as a " double monster," or (which the 

 distinctness of the '•'nuclei" seems to render more probable) have been the product of 

 the partial " fusion " of two originally separate disks, attached side by side to contiguous 

 parts of the same surface ; the vertical half-disk in either case being the joint product 

 of the two mutually-encroaching horizontal disks, whose continued increase at their line 

 of junction could only take place in this direction. In the large disk, represented in 

 PL VII. fig. 2, the peripheral folds are much deeper than are those of fig. 1, but the 

 central semi-discoidal outgrowth is smaller. There are, however, other considerable 

 vertical outsrrowths from the surface of the disk, the under side of which shows the same 

 exuberant productiveness. In the large disk represented in fig. 4 the central outgrowth 

 has the form of a small knob ; this, however, instead of being a solid mass of shell- 

 substance, has a properly " labyrinthic " interior, as is shown by the distribution of the 

 pores characteristic of that arrangement over the whole of its surface (fig. 4, h). One of 

 the peripheral folds extends itself as a vertical crest for some distance inwards, and four 

 other incipient half-disks arise from difi'erent parts of the surface, of which two have 

 united themselves together, as shown on a larger scale in fig. 4, a. Another large disk, 

 represented in fig. 5, shows a general crumpling of the margin, without the formation of 

 any well-marked vertical fold, with a small central knob and several iiTcgular protuberances 

 from the annuli forming the inner part of the disk. In the large disks represented in 

 figs. 6 and 7, the crumpling of the peripheral annuli is very strongly marked by the 

 production of vertical folds proceeding inwards towards the centre. In both cases the 

 growth of the disk seems to have been regular, up to a certain epoch marked by the 

 concentric elevation of the annuli, after which the crumpling appears to have commenced. 

 Such epochs are often indicated, even in the normal cbsk, as shown in fig. 3 ; and it 

 would not seem improbable that they mark some change in the external conditions of 

 the disks, which may have lived attached in their earlier stages, and have been afterwards 

 transferred by the action of the waves into situations more favourable to the production 

 of these outgrowths.^ 



^ Other examples of this " laciaiate " form, with a vertical section showing the divarication of two lamellse, and 

 the incompleteness of the partitioning of the last-formed annuli, will be found in PL. XVI. of Mr. H. B. Brady's Report 

 on the Foraminifera. 



