. The microscope and its revelations. s of this curious body, and especially its mostprojecting portions, are strengthened by a framework of thread-likecalcareous rods («). In this condition the embryo swims freely111rough the water, being propelled by the action of the cilia, whichclothe the four angles of the pyramid and its projecting arms, andwhich arc sometimes thickly set upon two or four projecting lobes(f) ; and it has received the designation of ////>•*. The mouth isusually surrounded by a soH of proboscis, the angles of which areprolonged into four slender processes (y, y,). s
. The microscope and its revelations. s of this curious body, and especially its mostprojecting portions, are strengthened by a framework of thread-likecalcareous rods («). In this condition the embryo swims freely111rough the water, being propelled by the action of the cilia, whichclothe the four angles of the pyramid and its projecting arms, andwhich arc sometimes thickly set upon two or four projecting lobes(f) ; and it has received the designation of ////>•*. The mouth isusually surrounded by a soH of proboscis, the angles of which areprolonged into four slender processes (y, y,). shorter than the fourouter legs, but furnished with a similar calcareous framework. The first indication of the production of the young Kchinus fromit* • plutens is given by the of a circular disc (fig. (, c) on one side of the central .stomach (/>): and this disc soonpresents live prominent tubercles (15). which subsequently becomeelongated into tubular processes, which will form the sucking- LARVAL ECHINI 899. feet of the adult. The disc gradually extends itself over the stomach,and between its tubules the rudiments of spines are seen to protrude(I)) ; these, with the tubules, increase in length, so as to project againstthe envelope of the pluteus, and to push themselves through it; whilst,at the same time, the original angular appendages of the pluteusdiminish in size, theciliary movement be-comes less active, by the actionof the suckers and spines,and the mouth of thepluteus closes up. Bythe time that the disc-has grown over half ofthe gastric sphere, verylittle of the pluteus re-mains, except some ofthe slender calcareousrods, and the numberof suckers and spinesrapidly increases. Thecalcareous framework ofthe shell at first consists,like that of the star-fishes, of a series ofisolated networks de-veloped between thecirrhi, and upon theserest the first formedspines (D). But theygradually become moreconsolidated, and extendthemselves o
Size: 1441px × 1734px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
