CHAPTER XXIII. 



OF THE CLASS OF ACALEPH^). 



1026. THE animals composing the class ACALEPH^: differ 

 widely in external form, and frequently, also, in the arrange- 

 ment of their organs ; so that it is difficult to assign any 

 character which shall be 

 applicable to them all. 

 Perhaps their most gene- 

 ral point of agreement is 

 the extreme softness of 

 their tissues, and their 

 free unattached condition : 

 by the former they are 

 distinguished from the 

 Echinodermata ; by the 

 latter from the Polypifera. 

 Although the radiated 

 structure is well marked 

 in the forms which we 

 may regard as typical of 

 this group (Fig. 610), 

 yet it is so entirely ob- 

 scured in others (Fig. 

 614), that, if they be re- 

 garded out of connection 

 with the rest, their claim 



to a place in this division of the Animal Kingdom would be 

 very doubtful. In general, however, it is not difficult to find 

 links of transition, by which the radiated forms pass into those 

 that are constructed apparently upon a different type ; and, 

 when this is the case, we should have no hesitation in uniting 



FIG. 610. PELAGIA. 



