JOURNAL OF MICROSCOPICAL SCIENCE. 



DESCRIPTION OF PLATES V AND VI, 



Illustrating Prof. Wy\'ille Thomson's paper on Synapta. 



PLATE Y.—Si/napfa inhcerens (O. F. Miiller, sp.) 

 Fig. 

 1. — Youug when first observed, June IStli, 1S61. 

 2. — Youug about a month later. 



3. — Diagram of the centre of the amb'jhtcral vascular system of the joung 

 iu the second stage; a, oesoj)h:igeal vascular ring; b, base of 

 ceecal process of the ambulacral vessel forming the cavity of one 

 of tlie tentacles ; <;, slit-like valve between the cavity of the ten- 

 tacle and the annular vessel; d, Polian vesicle; e, ambulacral 

 vessel accompanying one of the longitudinal muscular bands; 

 f, madreporic tubercle and canal. 



PLATE YI. 



1. — Base of one of the tentacles, showing the relation of parts; <?, one of 

 the calcareous plates of the oesophageal calcareous ring; b, central 

 ring of the ambulacral vascular system ; c, valve between the vas- 

 cular ring and the cavity of the tentacle, </; ^, Polian vesicle; 

 f, ambulacral vessel accompanying the longitudinal muscular 

 band, ;<; ^, peculiar cirrated bodies circulating in the ambulacral 

 vessels; /;, nervous ganglion ; k, large lenticular cells, imbedded 

 in the external sarcode layer ; /, contractile rosettes connected 

 with the layer of transverse muscular fibres, o; m, oval vesicl-es, 

 probably rudimentary organs of special sense; p, calcareous 

 "fibulae" imbedded iu the sarcode of the tentacular fringe; 

 q, miliary granules. 



2. — Upper portion of one of the longitudinal muscular bundles, showing 

 the relation of parts. 



3. — a — /, development of the "anchor" and "anchor-plate." 



4. — Network of anchor-plate just completed, before the deposition of the 

 external thickening layers 



5. — Perfect anchor and anchor-plate. 



6. — Irregular calcareous spiculse of the tentacles ; a, miliary granules. 



7. — Calcareous granules and rosettes at the anal extremity of the body. 



