546 
DR. CAEPEXTEE’S EESEAECHES OX THE EOEAMIXirEEA. 
mention has already been made 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 ufill 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, grj, gg') ; and the external 
walls of the chambers present an alternation of ridges and fuiTOws, 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. crisjpa, the diverging pair’s of branches fi’om each meridional 
canal open by minute pores on either side of the septal band, as is shourr in fig. I, and 
as will be readily understood from the relation of the parts as displayed in fig. 12. 
The subsequent formatioir of a calcareous deposit, continuous with that which solidifies 
the umbilical portion of the shell, upon the exterrral sru'face of the spiral lamina 
(*!]■ 185), renders the septal bands less distinct, and obliterates the ridges and firrrows 
of the intervening surface, as showrr in the portion h h' of fig. 1 ; and at the same 
time it carries the orifices of the divergiirg branches from the neighboru’hood of the 
septa into closer proximity with those of the branches proceeding fi’om 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. 1,?/', //') ; 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 difterent in character 
and position from the “ fossettes ” of P. aisjja, 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 supeificial 
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 mternal 
portions of the organism, as well as Avith the newer and more superficial ; this connexion 
being established by a series of branches that pass between the riA'o layers of the septa 
* This arrangement of the orifices of the diverging branches of the meridional canals is beautifully shown 
(as Mr. W. K. Paeker has pointed out to me) in the JS^auiihis striato-punctatus of Fichtel and Moll, which 
Mr. Parkee considers to be the Geoponus steUa-lorealis of Ehrexberg, but to be reaEy a Xonioniue 
form of Polystomella. See Ann. of Nat. Hist. ser. 3. vol. v. p. 103. 
