250 THE PREDOMINANCE 



enable one to determine whether the embryo, per se, is one of 

 the Zoophytic types, or is one of those worms (Tape-worms, 

 &c.) which bear a crown of hooks or suckers about the mouth, 

 or is a member of that group of Trepang-like worms to which 

 Bonellia (p. 216, fig. 126) belongs, and of which some possess a 

 circle of feelers at the end of the head. In fact, I have already 

 stated that some good naturalists persist to this day in classing 

 this latter group, the Sipunculacea, with the Holothuria (Tre- 

 pangs). 



If, however, we trace the development of these embryos, as 

 did the Norwegian naturalists from whose work these figures are 

 copied, we shall find that eventually, as the other parts of the or- 

 ganization become prominent, as they appear in this figure, (fig. 

 144,) they demonstrate by their arrangement a decided length- 

 wise lateral repetition (see the description of the figure at the 

 bottom of the page). 



In these other two figures, (figs. 145, 146,) which represent the 

 two opposite sides of the same individual, (an embryo Starfish,) 



one of them (fig. 145) has all 



the characters of a jointed 



worm, with its joints, as it 



were, strung on a longitudinal 



axis; nor does the other (fig. 



146) present a much less artic- 

 Fig. 145. ulate form than the former; 

 but yet for those who are familiar with the 



more advanced period of development. Considerably magnified. (See chap, 

 xvir. ZOOPHYTA, in the section on Holothuria.) A view of the lower side. 

 t, <l, the feelers ; m, the mouth ; /, the buccal ring ; aq, one of the sack-form ap- 

 pendages, Polian vesicle, of the circular aquiferous canal around the mouth ; me, 

 the madreporic canal ; aq*, aq*, the median longitudinal aquiferous canal ; aq, aq*, 

 the right and left inferior aquiferous canals ; s, s 3 , .s*, s 5 , the disciform ends of the 

 sucker-like feet (s 2 ) which arise from the lower median line of the body ; s 1 , the 

 aquiferous tube by which the feet are distended with fluid from the median vessel 

 (aq*) ; bd, the transverse muscular bands; the five longitudinal muscular bands 

 occupy the same place as the longitudinal aquiferous canals, (aq*, aq*,) each one 



