ORGANS OF SUPPORT, 



FIG. I. 



coloured, tuberculated animalcule exhibits in its interior nu- 

 merous smaller, round, spotted, and similarly formed beings 

 moving to and fro, as seen at A, and the entire volvox does not 

 change or vary its external form while it is seen swimming 

 about slowly with the enclosed young. When the exterior 

 capsule, or the parent animalcule bursts, as is represented at 

 B, and the young have escaped, we observe its fragments to 

 retain their original form with some degree of elasticity when 

 they are tossed about in the fluid by the motions of other 

 animalcules. We see the same transparent elastic integument 

 giving form, and support to the volvox morum, (Fig. 1 . C.) 

 which contains a much greater number of young in its interior, 

 and the same is seen also enveloping the separate globules 

 which compose the body of the gonium pectorals. (Fig. I. D.) 

 But the most distinct form .of the skeleton met with in 

 this class, is that which envelopes the body as a sheath, into 

 which the animalcule can withdraw its soft parts when 

 alarmed, and from which it can extend its ciliated anterior 

 portion for the purposes of nourishment, respiration, or 

 progressive motion. This vaginiform, exterior, thin, pellucid, 

 elastic covering is seen in the vaginicola innata, common in 

 sea water. This animalcule, formed like a vorticella, is seen 

 in Fig. 1. E, extending its ciliated anterior margin from the 

 opening in its sheath, and swimming by the action of its 

 cilia. The same animalcule is represented at Fig. 1. F with- 

 drawn into its transparent covering and fixed by its candiform 

 projecting posterior part. This form of the skeleton seen in 

 the vaginicola leads to the vaginiform horny coverings of 

 campanularue, and other forms of keratophytes. There are 



