226 GEKEKAL HISTOET OF THE IN^FUSOEIA. 



" The septa occupy (in OjperciiVina Arahica), transversely, about -^th of the 

 breadth of the chambers ; and each septum encloses within its walls two 

 calcareous tubes or vessels, one on each side, some little distance below the 

 contiguous sui'face of the shell (fig. 7 a, a); these we shall call inter septal 

 vessels. They are irregular both in their size and coiu'se, though generally 

 about -j-J^th of an inch in diameter, in the last-formed septa of a shell 

 having the dimensions of the one described, and diminish in calibre back- 

 wards or towards the fii'st-foiTned whorls. Each vessel commences in the 

 centre of an intricate network of smaller ones, spread over its own side 

 of the margin of the preceding whorl, and under the layers of the shell ; 

 these networks, which are joined together, we shall call the marginal plexus. 

 In its course each interseptal vessel gives off two sets of ramusculi, and the 

 marginal plexus one set. Of those coming from the interseptal vessel, one 

 set terminates on the siuface of the shell, particularly about the borders 

 of the septum ; the other goes into the walls of the shell, and through 

 the septum, to open probably on the inner surface of the chamber, while 

 the set from the marginal plexus opens on the margin. As this vascular 

 system appears to extend throughout every part of the shell, and must be 

 for the circulation of some fluids we will call it the interseptal circulation.''^ 



Prof. Wilhamson has likemse described a series of intraseptal canals in 

 Faujasina, and illustrated their arrangement by engravings. We have not 

 space to give the details, but can quote only the general results : — " The intra- 

 sejDtal spaces are vertical, and give off true divergent cylindrical canals from 

 their external margins, penetrating the thick parietes of the shell. These 

 spaces extend from the top to the bottom of each septum, and only assume 

 the form of canals when they approach the peripheral shell-walls. The con- 

 necting branches which unite the S2)aces of different convolutions are also 

 tubular. In no instance do these spaces or their divergent canals commimi- 

 cate with the interior of the segments (chambers) ; for the only dii^ect com- 

 mimications between the two parts of the organism are thi'ough the pseudo- 

 podian foramina, many of which open into the tubular portions of these 

 passages ; but never, so far as I have observed, into the intraseptal spaces." 

 Again, " the caidties in the translucent shell are thickly lined mth a dark 

 ohve-brown substance, which, if it be the desiccated soft animal, proves that 

 in this species the gelatinous tissue has not only filled the true chambers, but 

 has also occupied the intraseptal canals and passages. If this be so, it is 

 curious that the only medium of commimication betA^'ecn the soft tissues in- 

 habiting the spiral segments of the shell and those occupying the intraseptal 

 and central passages, should be the minute pseudopodian foramina .... It is, 

 however, ob\'ious that this organism supports the conclusion at which I arrived 

 in a previous memoir, viz. that the soft animal had the power of extending 

 itself externally far beyond the limits of any individual segment, and would 

 thus be able to secrete calcareous matter in other situations than the mere 

 parietes of its o^tl segment. It is only in this way that we can explain the 

 production of the dome-like covering which encloses the central umbihcal 

 cavities and their ramifying canals. But if it should be ultimately proved 

 that the soft tissues have occupied all these irregular cavities, we shall then 

 have a form of organization which, from its great variability of contour, ^vill 

 approach much more closely to the calcareous sponges than any hitherto de- 

 scribed." 



Schultze says that the species referred to by the two observers just quoted 

 have not come in his way, but that in none of the genera he has examined 

 has he met with a similar structure. He has been equally unsuccessful in 

 finding the interseptal spaces noticed by Carpenter in Nummulites ; and in 



