STACITEIA. 113 



ch.'imbcrlets. Exterior, granular or nearly smooth. Aperture terminal. Length -$ 

 inch (()'!) mm.). 



It may be a point still open to debate whether the uniserial subcylindrical forms 

 which constitute the group now to be considered should be regarded as pertaining to the 

 free moniliform type XwloximJla or to the essentially adherent Stacheia. The external 

 morphology taken by itself would lead in the former direction, and the species was 

 named at first in accordance, with that view ; but as material accumulated, and with it the 

 opportunity for more complete examination in respect to minute structure, the analogy 

 to the adherent type became more and more apparent. But even in external confor- 

 mation it is not difficult to trace a relationship between the apparently free species and 

 the simpler parasitic forms. In Stacheia pupoides for instance (PI. VIII, figs. 17 27), 

 it often happens that when the test grows upon any body narrower than itself, it 

 becomes more or less embracing, sometimes to such an extent that the ends of 

 the segments nearly meet on the other side. It seemed possible, therefore, that the 

 cylindrical Marginulina-\ke tests might have been originally parasitic, and have begun 

 life with the support of a central foreign body, which had subsequently more or less 

 completely disappeared either by disintegration or decomposition. The probability of this 

 view was strengthened by collateral facts, especially by the discovery of a much smaller 

 species, stouter in proportion to its length, and tapering symmetrically at both ends 

 (S.fusiformis), having similar internal structure, but with the foreign body frequently 

 remaining as an axial support. Supposing this explanation of the characters of Stacheia 

 marginulinoides to be the true one, the aperture still remains to be accounted for. If, as 

 it is safe to assume, the aperture of S. pupoides, like that of the trochoid Valvulince, is on 

 the under surface of the test, and 8. marginulinoides represents typically a similar form 

 with the segments completely embracing, it would follow that the aperture should be in the 

 interior close to the central column ; and in that case the pseudopodia would issue from the 

 end of the test. The actual structure is precisely in accordance with such a supposition. 

 Longitudinal sections show the central portions of the test confused in arrangement, the 

 septa often broken and not continuous, especially at the narrow end. This cannot be 

 gathered from any single specimen, for the sections must needs be axial, and the axis in 

 Stacheia marginulinoides is scarcely ever straight ; but it is not difficult to obtain clear 

 evidence from a series of preparations. The external orifice being, in point of fact, 

 the space left by the disappearance of the foreign body which formed the central 

 support, it is manifestly not essential that it should be at the broad end of the test, 

 and specimens actually occur (PI. VII, fig. 18, a, b, is an example) in which there is 

 no trace of aperture on the surface of the large terminal segment, whilst there is one 

 at the narrow end; and again, as shown in fig. 20, specimens may be found which have 

 two apertures, one at each end of the shell. 



It will be readily seen that, notwithstanding their close exterior resemblance to the 



15 



