HEMICHORDATA 



CHAP. 



name " Eichelwurm " used by German zoologists. But the idea 

 expressed by Delle Chiaje was really a similarity between the 

 collar of Balanoglossus and the outer shell of Balanus, the barnacle 

 or " acorn-shell " found everywhere on rocks between tide-marks. 



e FIG. 8. Metamorphosis of 



Balanoglossus, probably 

 of Balanoglossus bimini- 

 ensis Willey, Bahama 

 Islands. All the figures 

 are magnified to the same 

 scale ( x 14). A, fully 

 developed free-swimming 

 larva, or Tornaria, side 

 view ; B, commencement 

 of metamorphosis, side 

 view ; C, later stage, dor- 

 sal view. Increase in size 

 takes place after this 

 stage ; a, anus ; b.c', body- 

 cavity of proboscis ; c, 

 collar ; c.r, transverse 

 ciliated ring ; d.p (in A), 

 dorsal pore ( = proboscis- 

 pore), seen also in C on 

 the left side, just behind 

 the reference line p.c ; e, 

 eyes and sensory thicken- 

 ing of skin (in A) ; g, 

 gill-pore ; g.s, gill-sacs, 

 developing as outgrowths 

 of the alimentary canal ; 

 three are already present 

 in B, but are better seen 

 in C, in which they are 

 still without openings to 

 the exterior ; I, postern 1 

 part of the longitudinal 

 band of cilia ; I', its prae- 

 oral part ; both I and I' 

 are produced (in A) into 

 tentacles, over which the 

 band of cilia is looped ; 

 the groove in the middle 

 of the figure, between I 

 and I', conducts the food 

 by the transverse groove 

 to the mouth (m) ; />.<, 

 blood-space of proboscis 

 and pericardium ("heart " 

 of larva) ; s, stomach. 

 (After Morgan). 



Development. The free-swimming, larval stage of Balano- 

 glossus is known as Tornaria (Fig. 8, A). Several distinct forms 

 of the larva are known, 1 although it is not yet possible to refer 

 them with certainty to their respective adults. 



1 Spengel, Monogr. p. 370 f. 



