1891.] Embryology. 383 
der Synapta digitata (Jen. Zeit, XXII.) the author refers to the 
preoral ciliated band as arising from the adoral band (surrounding the 
mouth), and not from the other ciliated band, from which it is entirely 
separated, thus opposing the older view of Gegenbaur, adopted by 
Korschelt and Heider in their Lehrbuch. 
But the author’s present work, begun in April, 1890, at Helgoland, 
shows that the adoral band arises without connection with the preoral 
band, and that the union of their edges is secondary. Thus ontogenet- 
ically is given striking proof of the correctness of Gegenbaur’s sup- 
position, 
The stage where but a single ciliated band is present is called the Auri- 
cularia stage of the Bipinnaria, 
In older larvæ the postoral and preoral portions of the longitudina} 
(circumoral) ciliated band unite at the preoral apical pole, and form a 
median unpaired stripe. Later, on a plane parallel to the ventral sur- 
face, this median unpaired stripe divides, and thus forms thé preoral 
and postoral ciliated bands of the Bipinnaria. í 
The ciliated bands are formed by a loss of cilia and flattening of the 
cells over the rest of the body, thus leaving the bands as the only 
ciliated part. This process begins on the ventral side; the cilia dis- 
appear last at the apical pole. ; 
The adoral ciliated band is formed in a similar way, and at its 
anterior part comes into close relation, secondarily, with the preoral 
band. 
Thus is solved the only difficulty to Job. Miiller’s plan to derive the 
body form and arrangement of the ciliated bands for all Dipleurula 
larvæ from a fundamental type, since it is shown that the Asterid larva 
passes through an Auricularia stage, and that the preoral ciliated band 
is separated from an ancestral single ciliated band. This stage 
with a single ciliated band is the typical form, ontogenetically repro- 
duced in sufficiently young larve of all classes of Echinoderms. 
The author notes as an interesting fact that in Joh. Miiller’s com- 
parison the Ophiurid pluteus, by the increase of the posterior dorso- 
ventral bendings (auriculz of the Auricularia and Bipinnaria), to long 
and characteristic projections, in this important point stands nearer the 
typical form than the Echinid pluteus to which in other respects it is 
more comparable. 
He points out the close relation existing in all larvae between the 
upper transverse border of the preoral band and the adoral ciliated 
band. He believes that the Dipleurula larva cannot be traced back to 
the “ypical trochophore with preoral ciliated rings; probably not to the 
Am. Nat.—April_—6, 
