157 
the water, with the point of 
the arms resting against the 
underside of the surface film 
(— I suppose the faet that 
the cilia of the arms are di- 
rected upwards, as well seen 
on the figures in Théel’s 
Monograph of the develop- 
ment of Echiocyamas, e.g. 
* Fisj. 5. Larva of Echinocyamus pusillus, seen from 
PI. VI. Fig. 87 , aCCOUntS above. ^/i. a.l. antero-lateral arms; p.d. postero- 
for this* the ciliary move- dorsal arms ;p.o. postoral arms; n.nervous system, 
ment must then evidently produce an upward movement —). They 
may be found to rest so steadily in this position that it is possible 
to examine them with the, microscope (placing them in a small 
dish direetly under the lens), and I have thus been able not only 
to examine them from above with a rather high magnifying power, 
but even to make a camera-drawing thereof. (Fig. 5). The observ¬ 
ation of the larva in this position disclosed a peculiar semicircular 
band of nuclei closely arranged in a regular linear series, lying 
in the epidermis of the oral area, below the postoral transverse 
band and proceeding from there on each side in an arc towards 
the sides of the oral lobe, where it disappears. That this is really 
a larval nervous system, homologous with that of Auriculdria, I have 
no doubt, although I have not histologically demonstrated its nerv¬ 
ous character. The general structure is the same as that of the 
Auricularian nervous system, and as in Auricularia it lies in the 
circumoral area, the main difference being that in the Echino¬ 
cyamus larva it is an unpaired organ, while in the Auricularia’s 
it is a paired structure; also it is formed of a double series of 
cells in Auricularia , of a single series in the Echinocyamus larva. 
The position assigned to this nervous system in the first descrip- 
tion, mentioned above, is a mistake, due to the faet that the object 
was seen from the ventral side; in that view no clear idea could 
be gained of its true position. 
Flaving found this structure in the Echinocyamus larva I natur¬ 
ally looked for it also in the other Echinoid-larvæ available, viz. 
Echinus esculentus , Psammechinus miliaris and Echinocardium 
cordalum. In none of them I was able to discover anything cor- 
