CHAP. II. PRIMARY DIVISIONS OF TESTACEA. 37 



bodies, they are provided with processes like filaments ; 

 and there are 'generally two very short tentacula, at the 

 teimination of which are two black dots, representing 

 the eyes ; in this respect they certainly show a relation 

 to the Gasteropoda, but then their respiratory organs are 

 totally different. The Nudibranchia, in short, as their 

 name implies, have these organs arranged on the upper 

 part of their body, in the form of a rosette, so as 

 exactly to resemble a bunch of vine leaves, whose stalks 

 form a common centre. One, out of the three great 

 characters of the typical Testacea, is yet retained, for 

 the animal crawls upon its belly; but has lost the other 

 two, since they have neither a distinct head nor shell. 

 The tritons and dories have the additional power of 

 swimming and crawling on the surface of the sea, with 

 their foot uppermost : in the former case, they are pro- 

 pelled both by their branchia and the thin sides of their 

 body, which act in the manner of fins. 



(33.) Our next group is composed of those simply 

 constructed Testacea, which represent the Acrita in this 

 class, and which have hitherto been arranged among 

 that heterogeneous assemblage of animals, named Intes- 

 tina by Cuvier. Having now arrived at the most re- 

 mote limits of the Testacea, we find, in the order before 

 us, nothing more than faint indications, or, in other 

 words, the elements, of that organisation which belongs 

 to the typical tribes. The flattened disk-like form, 

 indeed, of the dories and the tritons is fully preserved 

 in the Planarite, and even in some of the FasciolcK ; 

 but the branchia, hitherto so variable, now become less 

 and less apparent, and finally disappear. Some of these 

 animals inhabit the water, but others are internal or 

 external parasites ; and this change of habit takes place 

 in groups so intimately connected in all other respects, 

 that we become convinced of the propriety of retaining 

 them in one and the same assemblage. Hence, without 

 venturing to determine the precise limits of the animals 

 which really belong to this class, we feel no hesitation in 

 considering a large portion of Cuvier's PARENCHYJHATA, 



