444 FORAMINIFERA, POLYCYSTINA, AND SPONGES. 



Fia. 208. 



Portion of Composile Aliiina! 

 type of OrbitoUtes CDinplanatiis :~a a', b b' 

 upper and lower annular bands of Iwo 

 ceniric zones ; c c, the upper layer of super- 

 ficial segments, and d d the lower layer, coU' 

 necled with the. annular bands of both zones : 

 €6, e'e', vertical segments of the two zones. 



of the simple type (Fig. 207). These indirectly connect together, 



not merely all the superficial cells 

 of each zone, hnt also the columnar 

 segments of the intermediate layer; 

 for these columns (c e, c <'} terminate 

 above and below in the annular 

 stolons, sometimes passing directly 

 from one to the other, but some- 

 times going out of the direct course 

 to coalesce with another column. 

 The columns of the successive zones 

 X^B^ UHL' ^Bl. 'HhJR' (t^vo sets of which are shown in the 

 '1^ mW^^^^L'TT Jl o figure) communicate with each 

 ^ ^Ti»: TlWr ffl^ ;ll.^ft. ° other by threads of sarcode, in such 



a manner, that (as in the simple 

 type) each column is thus brought 

 into connection with two columns 

 of the zone next interior, to which 

 complex it alternates in position. Similar 

 coif- threads, passing otf from the outer- 

 most zone, through the multiple 

 ranges of marginal pores, would 

 doubtless act as pseudopodia. Now 

 this plan of growth is so different 

 from that previously described, that there wcmld at first seem ample 

 ground for distinguishing the simple and the complex types as two 

 species. -But the tost furnished by the examination of a large 

 number of specimens, which ought never to lie ]ia,ssc'(l }ty when it 

 can possibly be appealed to, furnishes tliese very singular results : — 

 1st, That the two forms must be considered as specifically iden- 

 tical ; since there is not only a gradational passage from one to 

 the othei', but they arc often combined in the same individual, 

 the inner and first formed ]i(U'tion of a large disk fre(|uentlv pre- 

 senting the simple type, whilst the outer aiul later formed part 

 has developed itself upon the complex : — 2d, That although the 

 last mentioned circumstance would naturally suggest that the 

 change from the one plan to another may he simply a feature of 

 advancing age, yet this cannot be the case; since the complex 

 plan sometimes evolves itself even from the very first (the nucleus, 

 though resembling that of the simple form, sending out two or 

 more tiers of radiating threads), wliilst, more fretpu'iitly, the sim- 

 ple prevails for an indefinite number of zones, and then changes 

 itself in the course of a few zones into the complex. The mode 

 in which this change occurs is not a little curious. In the first 

 place, the short segments, threadc^d (so to speak) upon their an- 

 nular stolon, undergo elongation, and the annular stolon itself 

 becomes double, being first, as it Avere, split in two, and its upper 

 and lower halves being separated by the interpolation of a length- 



