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H. P. KJERSCHOW-AGERSBORG. 



4), or along a line drawn between vorderer Interradius-hinterer 

 Radius (Fig. i). 



Delage and Herouard claim that the relation of the madreporite 

 is far from being precise, and their orientation of the asteroid plan 

 corresponds to Ritter and Crocker's figures of young individuals, 

 if they be inverted. This is true, however, only in a general sense 

 for the madreporite which comes on the right side, but the anus 

 is placed in the same relative position in either case. This relation 

 is different in the adult. Here the madreporite is on the left ante- 

 rior side between the rays I. and V. and actually corresponds to 

 Ludwig's plan. But the so-called five primary rays of Ritter and 

 Crocker, which, according to Ludwig ('99), correspond to 3-IV., 



FIG. 4. Young individual, aboral view, in the eight-rayed stage (from Rit- 

 ter and Crocker) ; the sketch is inverted to show the probably anterior rays 

 (I-V) and their relation to the madreporite and the anus, nip, a, respectively. 

 A, the posterior primary ray. (Compare this figure with Figs. 6, 7, 8, 9). The 

 labeling is retained as in the original. 



2-III., i -II., 5-!. , 4-V., respectively (Fig. 6), for the larva and 

 the ground-plan of the common starfish, are not the posterior rays 

 in adult life of Pycnopodia, however, but the anterior rays. This 

 is easily seen in an actively moving individual, and may also be 

 readily learned from the study of the interpolation zones which lie 

 between rays 1 1. -VI., VI. -I. It seems quite reasonable that the 

 movements of Pycnopodia should be in the direction of, or along 

 the axis of, the oldest rays, with the oldest rays as determiners of 

 direction of movements. For, as I have shown before ('18), this 



