364 Mr. J. Hogg on Tentacular Classification o/*Zoophyte3. 



has hitherto been done towards explaining the causes of the 

 phaenomenon. When the above observations were made I was 

 not aware of any instance of a change in the direction of the 

 spiral; but since then. Professor Morren of Liege has pointed 

 out to me the occurrence of a double direction in the spire 

 formed by the twisting of the tendrils of Bryonia dioica ; and 

 I have subsequently observed in the tendrils of a species of 

 Passiflora a twisting not only in two opposite directions, but 

 in alternately different directions for five or six times to the 

 end of the spire. 



XLII. — On the Tentacular Classification of Zoophytes. By 

 John Hogg, Esq., M.A., F.R.S., F.L.S., &c. 



In his able and beautiful work on the ^ British Zoophytes,' 

 Dr. George Johnston has reviewed most of the classifications 

 that have as yet be«n brought forward for those extremely in- 

 teresting animals, which have been generally called Polypes 

 (Polypi) by most French naturalists, as well as for their struc- 

 tures or habitations, that have received, of late, the common 

 appellation of Polyparies (Polyparia) from the same writers. 



In the first place I may remark that three methods of clas- 

 sification present themselves to the investigator of this por- 

 tion of natural history ; first, that which is derived from the 

 Polyparies or dwellings of the animals ; — the second is taken 

 from the natural organization and forms of the animals alone, 

 that is to say, from the Polypes themselves ; and the third, 

 that method which may be founded on a combination of cer- 

 tain characters deduced both from the animals and likewise 

 from their dwellings. 



Now, as an example of the first method, in my sketch of 

 the ^ Natural History of the vicinity of Stockton-on-Tees,' 

 which was written in the spring of 1825, but not published 

 until the year 1827^ I introduced an arrangement of many of 

 our native Polyparies, grounded chiefly on the views of our 

 own illustrious zoophy tologist, the accurate Ellis ; and in order 

 that it may be clearly understood, I trust I may be pardoned 

 for here subjoining an outline or synopsis of it. 



