OF BILATERALITY. 251 



young of this group, there is sufficient of the starfish physiog- 

 nomy about its anterior end, to enable them to refer it to its 

 proper place among the Zoophytes. 



Here, again, in these two figures (figs. 147, 148) of a young 

 worm, the younger one (fig. 147) shows scarcely 

 the trace of articulation, whilst its 

 bilaterality is prominently set forth 

 by the pair of eyes, and the two 

 right and left groups of vibratile 

 Fig. 147. cilia (a). In the older one (fig. 148) 

 it is clear that the jointed structure of the body is Fig. 148. 

 superimposed upon a bilateral basis ; for it is still quite as evi- 

 dent as in the younger one, that not only the eyes, but also the 

 groups of vibratile cilia (a) are arranged in reference to a right 

 and a left, notwithstanding the partial obscuration of this feature 

 by the prominency of the articulation. 



Finally I will recall to your minds the young worm-like Mol- 

 luscan, (fig. 149,) simply to show how little it resembles its adult 

 state, as represented in this figure, (fig. 150,) and yet how strictly 

 it conforms to the bilateral type. 



If, now, we turn to the lowest forms of each grand division, 

 we shall find this idea carried out in another guise. This will 



of the latter lying in a furrow along the middle of one of the former ; </ 3 , the 

 cloaca, a saccular enlargement at the posterior end of the intestinal canal. 

 From Koren and Danielssen. 



Fig. 145. A view of the back of a worm-like embryonic stage of a Starfish. 

 Magnified about 40 diameters. From J. Mutter. 



Fig. 146. A view of the front side of the same as in fig. 145. s, the sucker- 

 like feet in an incipient stage of growth; a, the end of one of the five short, 

 blunt, rounded arms, from which s arise ; &, c, the joint-like divisions of the body. 

 From J. Miiller. 



Fig. 147. Protula elegans. M. Edw. Highly magnified. A view of the 

 back of a young marine worm, in its earliest stage, at the moment of its birth, 

 a, the groups of vibratile cilia at the anterior end ; b, the posterior end ; the 

 eyes are two dots just in front of a. From M. Edwards. 



Fig. 148. The same as fig. 147, in a more advanced stage of growth, a, b, 

 as in fig. 147. From M. Edwards. 



