SERTULARIA. 170 



colour, as while contained in the vesicle, not exceeding the third or fourth 

 of a line in length, and during progression, shaped somewhat as a double 

 cone or shuttle, but becoming linear as its motion relaxed. 



Having heard some accomplished naturalists dispute the animation of 

 the beings which are here designed planulse, I am now describing, as pre- 

 viously and as I mean to do subsequently, such facts as bear testimony 

 of it. We cannot be too scrupulous in admitting what seems an absolute 

 metamorphosis without unchallengeable evidence. On weighing the import 

 of the whole, the reader can exercise his own judgment. 



This active motion of these and other planulse indicated the presence 

 of some external organs whereby it was effected. Yet on subjecting many 

 of all kinds to the microscope, none such could be discovered. Neither 

 have I been able to detect any cilia or ciliated apparatus on the contents, 

 whether more or less mature, of the most transparent vesicles of the Ser- 

 tularise. Possibly the powers employed were insufficient ; but we know 

 very well, at the same time, that the vermicular tribes are capable of very 

 speedy motion without similar external auxiliaries, that mere undulatory 

 alterations in the body are enough. 



No planulae had appeared on April 26, in a vessel set apart with spe- 

 cimens of the Serhdaria falcata on the 23d ; but 30 or 40 were seen next 

 morning. Several corpuscula also occupied the bottom, and a very few 

 were floating — circular under the microscope, of a greyish-yellow tinge, and 

 about a third less than the extended planulse. The number of planulse 

 increased so much next day, that portions of the vessel seemed yellow from 

 their accumulation : many moving swiftly, others were contracting, fig. 7. 

 On the 5th of May not one could be seen. 



Meantime nascent Sertulariae were springing every where, but chiefly 

 on the bottom ; they were also on the sides, some as high as the surface 

 of the water. Many vesicles now appeared empty ; yet the numerous 

 brood still continued to be so much augmented, that although the vessel 

 could not have contained above three ounces of water, at least 200 origi- 

 nating Sertulariaj were dispersed within it on May 13. 



Spines rose as usual from circular spots ; cells were generated on their 

 summit, whose tenants, perfectly white, exhibited a long neck, and about 



