66 



• 

 the before mentioned muscles are attached. All 3 pieces come while undergoing this change 

 closer together; and the articulation between the side-pieces and the middle-piece is effected 

 in the manner which characterises the developed pedicellariae. The changes described affect 

 only the calcareous particles which develop themselves in the interior of the pedicellaria?, and 

 which therefore are to be considered as a secretive product of the plasma of the original 

 cell. The soft surrounding parts, or the cuticular sheath, are formed immediately by a simple 

 readaptation of the whole cell. Already in a very early stage of development, there may be 

 observed (see fig. 34), on the exterior side of the cell, a slight insiuuosity like an incipient 

 division. This insinuosity becomes little by little deeper and deeper, and represents at last 

 a deep incision dividing the cell, into 2 broad lobes, each of which includes the anterior 

 extremity of one of the side-pieces. These lobes unite themselves, during the further deve- 

 lopment, directly with the 2 movable flaps of the pedicellaria. At the same time the whole 

 cell, formerly sunk in the skin, rises little by little, above the surface, so as at least only to 

 remain attached to it by a thin continuation, which becomes the flexible stem whereby the 

 pedicellaria is fastened to the skin. When this stem is fully formed, then all the other 

 parts belonging to the pedicellaria have also attained their definitive development: and it 

 now begins to participate in the common function of all these small organs, to seize and 

 hold fast all objects that come in connexion with them. 



B. Divergent development. 



The phenomena of development noticed in the preceeding lines are such as are 

 common to all individuals, and generally do not only apply to the whole genus Brisinga, 

 but partly also to all the other star-fishes. We come now to a series of changes which 

 usually do not take place until the animal has attained a much more advanced age, and 

 which go in a more divergent direction. These changes manifest themselves as more or less 

 distinctly marked differences in the external form of the body, and in the particular details, 

 between the different individuals. We have again to distinguish the more ordinary deviations 

 from those dependent on quite accidental causes, and therefore to be regarded as more 

 abnormal deviations. 



a. Individual variations. 



On examining a series of individuals, it will soon be found that the individual varia- 

 tions in the present species range within tolerably wide limits. The variations apply partly 

 to the number of the arms or ambulacra, partly to the form and arrangement of the diffe- 

 rent appendages belonging to the skin, and partly to the color. 



