546 DE. CAEPENTEE'S EESEAECHES ON THE FOEAMINIFEEA. 



mention has already been made (*f[ 184), the prolongations of sarcode which occupy the 

 diverging branches there passing into the stolons which connect the adjacent segments. 

 It will be easily understood, however, that the position of the external orifices of these 

 diverging branches will depend upon the thickness of the spiral lamina which they have 

 to traverse before gaining its surface. In the newest portion of a shell which has not 

 yet attained its full growth, we find that lamina comparatively thin ; its surface is 

 distinctly marked by the septal bands (Plate XVIII. fig. 1, gg*, gg') ; and the external 

 walls of the chambers present an alternation of ridges and furrows, passing directly 

 across from one septal band to another, the ridges corresponding to the grooves of the 

 internal surface that receive the "retral processes" (^[ 185), and the furrows with the 

 internal ridges that separate these grooves. Into these furrows, which represent the 

 deeper "fossettes" of P. crispa, the diverging pairs of branches from each meridional 

 canal open by minute pores on either side of the septal band, as is shown in fig. 1, and 

 as will be readily understood from the relation of the parts as displayed in fig. 12. 

 The subsequent formation of a calcareous deposit, continuous with that which solidifies 

 the umbilical portion of the shell, upon the external surface of the spiral lamina 

 (^f 185), renders the septal bands less distinct, and obliterates the ridges and furrows 

 of the intervening surface, as shown in the portion h h' of fig. 1 ; and at the same 

 time it carries the orifices of the diverging branches from the neighbourhood of the 

 septa into closer proximity with those of the branches proceeding from the adjacent 

 meridional canals. As the diverging branches enlarge greatly in diameter with their 

 augmentation in length, their superficial orifices become more and more conspicuous; 

 each is surrounded by a little pit or depression of its own (fig. l,n', H'); and the rows 

 of these depressions, when the spiral lamina has acquired its full thickness, constitute 

 the only markings which it presents, the septal bands being completely obliterated, as 

 is best seen on the surface of one of the interior whorls, exposed by the removal of 

 that which covered it. It is obvious, therefore, that these depressions, which are 

 related only to the distribution of the canal-system, are essentially different in character 

 and position from the " fossettes " of P. crispa, which intervene between the ridges that 

 cover-in the retral processes ; but they have this in common, that the orifices of the 

 diverging branches are to be found in both of them ; and the removal of the superficial 

 portion of the spiral lamina, even when thickest (which may easily be accomplished by 

 the assistance of dilute acid), brings back these orifices, in P. craticulata, to the 

 immediate neighbourhood of the septal bands, which then again become apparent*. 



190. The meridional canals are further connected with the older and more internal 

 portions of the organism, as well as with the newer and more superficial ; this connexion 

 being established by a series of branches that pass between the two layers of the septa 



* This arrangement of the orifices of the diverging branches of the meridional canals is beautifully shown 

 (as Mr. W. K. PABKEE has pointed out to me) in the Nautilus striato-punctatus of FICHTEL and MOLL, which 

 Mr. PAEKEB considers to be the Geoponus stella-lorealis of EIIEENBEBG, but to be really a Nonionine 

 form of Polystomella. See Ann. of Nat. Hist. ser. 3. vol. v. p. 103. 



