The porifera and coelentera . the development of the canal system in theseforms is a stage which has advanced considerably beyond theOhjnthu^i condition, and conforms more to the second type of canalsystem (Fig. 76 ; cf. Fig. 44), the gastral layer being folded toform flagellated chambers. The wall of the sponge even in these * Fossil forms: Tr. = Trias, Jur. = Jurassic, Ool. = Oolite, Cret. = 112 SPONGES early stages consists of five layers (Figs. 76, 77): (1) an outerporous skin, the dermal membrane {); (2) within this is a spacetraversed in all directions by strands of tissu
The porifera and coelentera . the development of the canal system in theseforms is a stage which has advanced considerably beyond theOhjnthu^i condition, and conforms more to the second type of canalsystem (Fig. 76 ; cf. Fig. 44), the gastral layer being folded toform flagellated chambers. The wall of the sponge even in these * Fossil forms: Tr. = Trias, Jur. = Jurassic, Ool. = Oolite, Cret. = 112 SPONGES early stages consists of five layers (Figs. 76, 77): (1) an outerporous skin, the dermal membrane {); (2) within this is a spacetraversed in all directions by strands of tissue, which constitutethe suhdermal trabecular latjcr (); (3) within this is a continuouslayer of thimble-shaped flagellated chambers, the blind ends ofwhich are turned towards tlie dermal surface, and their oj)eniiigstowards the gastral cavity (/.<?); (4) internal to the chambers isanother space, traversed by the ;fr(d layer of trabeculae {),quite similar in its structure and appearance to the subdermal. Fio. 76. Longitudinal SPCtion of a young specimen of I/inugineUa pu)xi, , with commencingfurmation of the oscular area. The spicules are omitted from the drawing. x35. (After F. ) , dermal membrane ; , subilermal trabecular layer ; /.c, flagellated chamlxT ;, subgastral trabecular layer ; , gastral membrane ; (>.(, gastral cavity ; osc, region offuture osculuni. layer; (5) and finally, the gastral cavity is limited by a porousgastral mcmjn-auc (), whicli recalls in its structure the dermalmembrane. Of these five layers, the tliird comprises tlie wholegastral layer; the first, second, fourth, and fifth are ditlerentia-tions of the dermal la3er. The five layers that have been described recur in the same orderand with similar characters in the body wall of all Ilexactinellids,which a n-markable uniformity in this )ect. Thechief modifications that are met with in the canal system are due SPONGES either {a) to a
Size: 1311px × 1906px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
