MUSEUM OF COMPARATIVE ZOOLOGY. 193 
Holothurians the body girt by several parallel belts of cilia. One only of 
these rings of large cilia remains unchanged in Tornaria and in Pilidiwm recur- 
vatum ; but in the former genus two others, very much modified in position 
and never parallel, form the loop-like bands between which the mouth opens. 
These bands, quite simple, as I shall later show in the young Tornaria, have a 
very tortuous course later in their career, but never attain the complexity 
which marks the course of homologous bands on the young of our common 
Starfish or Sea-urchin. Much greater than its resemblance to the young Echi- 
noderm is the likeness of our new Pilidiwm to the well-known Tornaria. 
On the same plate with my figures of the larve of P. recurvatwm are 
introduced for a comparison two illustrations of very young stages in the 
growth of Tornaria (Balanoglossus). These are still younger than any larve 
which are yet known of our American Tornaria, and present many very inter- 
esting features. The closeness of the relationship between them and the 
younger members of the series of Pilidiwm which they accompany is not the 
least interesting of the many comparisons which they suggest. 
In the youngest (Fig. 16) we have a Tornaria of an irregular pear-shaped 
form, with well-marked cesophagus, stomach, and intestine. A mouth opens 
on one side of the body and an anus is found at its lower pole. The external 
surface of the body is crossed by two simple ciliated bands. These have a 
common union at the upper pole of the larva, but a very divergent course on 
its external surface. The shorter of these ciliated bands forms a loop varying 
slightly from the form of a ring, which extends from the upper pole nearly to 
the equator, but never into the lower hemisphere. The larger band has a 
more tortuous course than the other, which it resembles in its loop-like form. 
It is much longer, and extends into the lower hemisphere almost to the lower 
pole. It meets in its course the smaller band only at one point, which is at the 
upper pole of the embryo. The mouth opening of the young Tornaria lies on 
its equator under the eaves of a projecting upper hemisphere, and between 
these two ciliated bands. At the common junction of the two ciliated bands 
is found a pair of eye-spots, above which rises a small tuft of cilia. The Tor- 
naria swims with this region uppermost in the water. From that part of the 
larva upon which these ocelli are borne, extending internally to the neighbor- 
hood of the union of esophagus and stomach, passes « muscular thread very 
similar to like threads already mentioned in Pilidiwm. An unpaired tube 
extends from the point of union of the esophagus and stomach, on its dorsal 
side, to the middle of the dorsal flexure, opening externally by a “dorsal 
pore” about diametrically opposite the mouth. The sac or enlargement of 
this tube at its inner terminus has not yet reached any great size. 
In this youngest Tornaria there are, as appears also in Miiller’s original 
description of Tornaria, no ring of large cilia near the anal pole and no lateral 
bodies (‘‘ lateral plates,” “lappets,” A. Agassiz) by the side of the stomach, 
such as we find in the older Yornarie. All theoretical questions which 
consider a comparison of these last bodies to the water-tubes of the Star- 
fish larvae must take cognizance of the fact that the median water-tube, which 
VOL. XI.—NO. 9. 18 
