144 DESCRIPTION OF {Polygastrica. 



vations have appeared, in No. xxxiii. of the Annals of 

 Natural History, by Mr. Dah-ymple, from which I select 

 the following : my intention in this work being not to 

 confine it to my own views^ but also to record those of 

 others, believing that, by so doing, I shall best serve the 

 public, and advance this science. 



Mr. D. describes the Closterium as consisting of " a 

 green gelatinous and granular body, invested by a highly 

 elastic and contractile membrane, which is attached by 

 variable points to a hard siliceous shell." This lorica, 

 Mr. C. Varley states, will resist even the action of boiling 

 nitric acid. The form of Closterium is spindle-shaped 

 or crescentic, the shell consisting of two horns, taper- 

 ing off more or less to the extremities, and united 

 at the central transverse line, constituting a perfectly 

 symmetrical exterior. At the extremity of each horn is 

 an opening in the shell, which, however, is closed within 

 by the membranous envelope — wanting, however, in some 

 specimens. Within the shell, and at the extremity of the 

 green body, is a transparent chamber, containing a vari- 

 able number of active molecules, measuring from the 

 20,000th to the 40,000th of an inch ; these molecules, 

 or transparent spheroids, occasionally escape from this 

 chamber, and circulate vaguely and irregularly between the 

 periphery of the gelatinous body and the shell. Further, 

 the parieties of this chamber have a contractile power. 

 The author denied the existence of any papillae or probos- 

 cides at this part, as well as the supposition of Ehrenberg, 

 that these moving molecules constitute the bases of such 

 papillae. He also denied the statement of the same dis- 

 tinguished observer, that if colouring matter was mixed 



