206 



NANOMIA CAEA. 



tremity, and being perfectly colorless ; this tentacle is three or four 

 times the length of the polj'p, and is covered with patches of small 

 lasso-cells scattered irregidarly over its surface ; the walls of this poljqs 

 are thick, and are not capable of extensive expansion or contraction, or 

 of any remarkable alteration of shape, as the former kinds. There is 

 still a fourth kind of appendage formed here and there along the stem, 

 one of which is figured on the top of Fig. 338, which resembles this 

 last kind of polyp, being closed, like it, at the extremity, but having 

 neither scale nor tentacles of any kind, and in the proximal end of 

 which we notice an accumulation of oily matter ; these I simjjly men- 

 tion here, and shall return to them hereafter. 



The new polyps which are added to the community take their origin 

 from the cluster of buds situated beneath the swimming-bells ; like the 

 swimming-bells, they are formed by the bulging of the wall of the main 

 axis (Fig. 342) ; they very soon assume the general aspect of feeding 



polyps, though they remain 

 closed at their distal extremity 

 after they have attained a con- 

 siderable size {p, p', p", Fig. 

 342) ; the scarlet pigment-cells 

 make their appearance at a 

 very early period, so that we 

 are able, in very young buds, 

 to recognize the nature of the 

 future polyps ; as soon as the 

 polyp buds are slightly more advanced than they are in the figure here 

 given (Fig. 342), the nature of the tentacular buds at the base, and the 

 total absence of pigment-cells in some of the larger closed buds, enables 

 us readily to decide to which kind of polyps (Medusae) these diflFerent 

 buds will give rise ; the peculiar sole-shaped knobs of one of the kinds 

 of tentacles are nothing but an expansion of the original diverticulum 

 at the base of the polyp ; the diflFerent phases through which the knobs 

 pass are very easily followed by examining the various stages of growth 

 found in a cluster of tentacles, such as is represented in Fig. 338 (some- 

 what enlarged in Figs. 343, 344), until they attam the shape repre- 

 sented in Fig. 339. They are at first a narrow bag, with a few scat- 

 tered lasso-cells (a, Fig. 343), then the thickness of the wall at the 

 extremity increases, the lasso-cells at the same time becoming large 

 (6, Fig. 343). In the next stage, when seen in profile, the sac has 

 assumed a hook-shajoed form (c. Fig. 343), the bend becomes still more 

 marked, and the lasso-cells ' are now arranged in a row along the ex- 

 tremity [d, Fig. 343) ; the walls become thicker as the lasso-cells 



Fig. 342. Cluster of MedusEE (feeding polyps) in different stages of development, before the 

 appearance of the scale or of the tentacles, p, oldest ; p', somewhat younger ; p", still younger. 



