118 



mouth is situated in one of the interradial areas, — not in the ambulacra! 

 centre, as it is in the adult forms of the existing Echinodermata. 



Fi^. 78, Fig. 79, fig. 80, 



Fig. 81. 



Fig. 78 Jjijiinnaria as-terigera Sars, (copied frcm Jl'iiller),, 

 r/, the stomach ; part of the body of the larva : c, r.mlbula- 

 cral centre, position of the permament mouth, in this stage not 

 open ; one of the five ambulacral canals ; ^, sand canal,/, 

 madreporic plate ; w, entrance into the stomach ; o, oesopha- 

 gus ; 7>, larval mouth or pseudostome ; r, oesophageal ring ; i\ 

 vent 79 Ideal figure described below. 80 Codonites steUiformis, 

 oblique view to show both body and summit. 81 Summit of 

 fig. 80. 



In Bipinnaria asterigera Sars, according to Miiller, the digestive cavity 

 is a sub-globular sack without any extension sinto the rays, as there are in 

 the adult Star-fishes. The oesophagus, fig. 78, o, is a fleshy, consisted tube 

 ■with a large mouth or pseudostome, It passes through the [wall of the 

 stomach by an opening somewhat smaller than the mouth, and situated in 

 one of the interradial spaces at m. The madreporic plate, /, and sand 

 canal, e, the latter holding the convoluted plate (when it occurs), are 

 situated above the orifice, m, and between it and the ambulacral centre, c. 

 The circular space at c, is undoubtedly the homologue of the central space 

 in the apex of Nudeocrinus, figs- 73 and 75, and of Codonites, figs. 80 and 

 81. It is also the position of the mouth in the adult Star-fish ; but in the 

 larval stage it is completely closed by the soft external skin and sarcode of 

 the body. In the fossils it is also closed, but by an integument of thin 

 calcareous plates. The Bipinnaria is nourished by minute particles of 

 matter difi*used through the water, and drawn into the digestive sack 

 through the mouth and oesophagus by the action of internal ciha. I beheve 

 that all the fossil Crinoidea, Blastoidea and Cystidea, ingested their food 

 in this way, and without any aid whatever from the arms or pinnulse. 



Perhaps there is no embryologist who will not admit, that it is possible 

 for an animal like Bipinnaria to develop organs of reproduction and 



