89 



preoral lobe bending downwards over the oral area so as to cover the 

 mouth openini* completely, the entrance to the mouth being the narrow 

 slit left between the anal area and the projecting frontal area. The eso- 

 phagus is short, somewhat folded (comp. Species f, PI. XIII. Figs. 3— 4); 

 the stomach is very large, filling almost the whole body; the rectum appears 

 to be small and short, situated in the lower part of the body, apparently 

 within the space limited by the posterior and the supplementary ventral 

 transverse rods. I have, however, been unable to make out its shape 

 quite distinctly, and hkewise the anal opening could not be located. The 

 development of the enterocoel and 

 hydrocoel could not be made out; 

 a single specimen in a younger stage 

 is, unfortunately, in too poor a con- 

 dition for showing anything of the 

 enterocoel or hydrocoel formation; 

 it does, however, show that the oral 

 lobe is quite narrow and somewhat 

 elongate, so that from the beginning 

 the mouth-opening is free, the oral 

 area being not yet covered up by 

 the preoral part of the body. This 

 then takes place in a somewhat 

 later stage, though still rather early, 

 being completed already before me- 

 tamorphosis is beginning (Fig. 29). 

 In the course of the i)rocee(ling metamorphosis the body becomes quite 

 oblique, the whole anterior part being pushed over to the right side, as 

 seen in the figures of species f. 



The skeleton (Figs. 34 — 35). The postoral rods difler markedly from 

 those of species a— d in having only very small holes, the unfenestrated 

 part of the component rods being considerably larger. They are entirely 

 smooth. The body rod is quite short, at the point widened into a large 

 fenestrated plate (Fig. 35), to which the abductor muscle is attached. 

 Seen in ventral or dorsal view this plate appears as a thin, slightly out- 

 wards curving rod; seen from the liind end of the body (Fig. 34 A) it 

 is found to be directed somewhat towards the dorsal side. The ventral 

 transverse rods are entirely lacking; the ventral recurrent rod is quite 

 short. The supplementary ventral transverse rod is highly developed, 

 dividing in the end into two branches, one upwards directed apparently 

 having the shape of a simple thorn, but really, as may be seen in side view, 

 having the shape of a small, mostly fenestrated plate, to which the ventral 



Fig. 35. Half of the body skeleton of Echino- 

 pliiieus transversus, species e, seen from the 

 side; showing I he widening of the body rod (b.). 

 The postoral rod (po.) has Ijeen cut close to 

 its l)ase. al. the rudimentary anterolateral 

 rod; t. the thorn to the point of which the 

 dorsal adductor muscle is attached; sir. sup- 

 plementary ventral Iransverse rod. vr. ventral 

 recurrctit rod. '*"/,. 



