214 



HYATT 



of the opacity of the sheaths of the specimens of Fredericella 

 regina, upon which my investigations were principally 

 made, to determine with absolute precision, whether these 

 conical projections were tubes, or partly solid muscular 

 bands connecting the investing membrane with the overly- 

 ing layer (Fig 1, a). 



The cellular contents do not project into the interior of 

 the cones, as they might be expected to do, if the latter 

 were simply hollow continuations of the investing mem- 

 brane. This fact may be considered as favoring the opin- 

 ion, that they are partly solid, and, perhaps, muscular, con- 

 nective bands, or else there must be another membrane in- 

 terior to the one described, which, also, invests the cellular 

 contents and prevents the cells frofn flowing into and fill- 

 ing up the conical projections. The overlying layer (Fig. 

 1, a) is exceedingly thick, and acts, in all respects, like a 

 muscular membrane. It is unconnected with the horny 

 sheath, and either lies closely against the latter, or is sepa- 

 rated from it; and may be smooth and of equal thickness 

 throughout, or corrugated and of unequal thickness, as in 

 fig. 1, according to its state of expansion, or contraction. 



The horny sheath is composed of flattened, hexagonal 

 cells, the whole surface garnished internally with a thin 

 coating of short, horny, brown colored setae (Fig. 1, W). 

 This sheath is so exceedingly tough and hard that it is 

 difficult to pierce it with the point of a needle. 



The annuli of the statoblasts of Plumatella, and of the 

 other genera in which they are found, are made up of more 

 prominent and larger hexagonal cells than those of the 

 horny sheath. 



In Fredericella the annu- 

 lus is not developed, but in 

 ail the other genera it is, and 

 in Pectinatella and Crista- 

 tella spines are superadded. 



These spines apparently 

 arise from the annulus in 

 Pectinatella, as described 

 by Dr. Leidy, but they 

 may be traced by a close 



FIG. 1. Section of the end of a sta- 

 toblast of FKEDERICELLA REGINA ; &, 

 conical projections on the surface of the 

 cellular contents; a, thick, muscular 

 membrane ; >', horny sheath. 



