382 Mr. Hogg's Observations on the Spongilla fluviatilis, 



ness I had the pleasure about eighteen months ago to Avitness the living polypes 

 in that Zoophyte, and to observe for the first time the actual presence of the 

 cilia ranged along their tentacula, and the extremely rapid and vibratory mo- 

 tions of those organs in the water. That author has made known many 

 curious and important facts respecting the Binosculous Ciliotentacular Zoo- 

 phytes* in his interesting memoir, which is published in the Philosophical 

 Transactions for 1837, where, at p. 412, writing on the gemmules of that spe- 

 cies, he says, " It would be impossible to explain the variety of motions which 

 the gemmules are capable of executing, were it not obvious how complete is 

 their control over the action of the cilia, which are their sole locomotive or- 

 gans. They generally swim with the convex part forwards, and with the 

 greatest rapidity. Sometimes they simply rotate upon their axis, or they 

 tumble over and over; or, selecting a fixed point, they whirl round it in rapid 

 circles, carrying every loose particle after them. Others creep along the bot- 

 tom of the watch-glass upon one end, and with a waddling gait ; but generally 

 after a few hours all motion ceases, and they are found to have attached them- 

 selves to the surface of the glass." He further adds, " The parenchyma of the 

 gemmules has a contractile power, somewhat like that of Hydra, but less in 

 degree, by which the form of the body is occasionally altered." 



* These are the Ciliobrachiate Polypi of Dr. A. Farre. I have long considered the tentacles 

 (tentacula) of Zoophytes as presenting the principal and most characteristic organs by which those 

 animals ought to be classified in strict accordance with their natural conformation. The Ciliotentacula 

 would include a large and separate order, composed of the genera Flustra, Cellularia, &c. The Pi/mi- 

 tentacula would comprise those Zoophytes whose tentacula are pinnated ; for instance in the Gorgonim, 

 Pennatulœ, &c., where the tentacles are furnished with small pinnse. The Tubitentacvla, the Actinia, 

 the Madreporœ, and the rest which possess tentacula in the form of siphons or hollow tubes perforated 

 at their extremities. The Planitentacula, which is synonymous with a part of Dr. Farre's Nudibra- 

 chiate Polypi, would comprehend those Zoophytes whose tentacles are quite plain and devoid of any 

 lateral excrescences or appendages, as Tubularia, Coryne, &c. ; and the order Noditentacula, the genus 

 Hydra, and family of the Sertulariadœ, which have those organs covered with little knots, nodules, 

 or projections. But the class ^^ooyj/zy^o itself should be divided into two subclasses ; viz. 1. Binoscitla, 

 or the Zoophytes that have distinctly two holes or orifices, one of which is their mouth, and the other 

 their anus ; to this belongs my first order. And 2. Unoscula, those with one orifice, serving both for 

 their mouth and anus ; herein are supposed to be included all the four latter orders. Additional ex- 

 aminations, indeed, guided by some anatomical skill, are yet wanting for the purpose of completing 

 this tentacular arrangement, which would then be of considerable use in more clearly defining several 

 of the most important characters that belong to those very remarkable animals. 



