MUSEUM OF COMPARATIVE ZOOLOGY. 185 
Lepidonotus squamatus (?). 
Plates III. and IV. 
The youngest * larva (Pl. IV. Fig. 14) of this genus is monotrochal. The 
body has a globular shape, upon which the arrangement of the circle of cilia is 
not perfectly equatorial. The pole of the cephalic hemisphere is pointed, and 
bears two eye-spots connected over the dorsal surface of the preoral lobe by a 
double row of pigment spots. Parallel with the mesial circle or circles of cilia 
are two rows of pigment spots on the upper and two on the lower (posterior) 
hemisphere of the body. The lower half of the embryo is more elongated than 
the upper. The mouth is widely open, and lies just below the rim which 
bears the larger cilia. The lower lip is fringed with a row of smaller cilia. 
The interior of the larva is occupied by a stomach, cesophagus, and intestine, 
which are not clearly differentiated from each other. 
The next oldest larva (Figs. 16, 17), Lepidonotus, is characteristic.t The 
body has elongated itself, although it has not yet become worm-like in shape.. 
The oral lobe is hemispherical, without appendages, and bears scattered cilia 
upon the pole. There are four eye-spots arranged in two pairs. The body 
bears three pairs of lateral appendages, and the terminal segment is prolonged 
into two short protuberances. When seen from below, each of these will 
be found to consist of a single appendage, from which arises a bundle ot 
spines. Each of these spines ends in a small tooth and a short terminal ar- 
ticulation (Fig. 16,a). Upon the back of the larva we find rudiments of the 
elytra as diminutive circular plates hanging from the bases of the parapodia, 
which, however, do not cover these bodies. The interior of the larva is taken 
up by an cesophagus, a large stomach, which fills most of the preoral lobe and 
extends downward in the body cavity to the second appendage (parapodinm), 
and a long, straight, narrow intestine, which diminishes gradually in size from 
its union with the stomach to the vent. Cephalic appendages first appear in a 
larva a little older than the last. (Pl. III. Figs. 1,2.) The first of these to arise 
is the median antenna, which first appears as a stout median protuberance of 
the cephalic walls on the dorsal side of the head between the eye-spots. The 
larva now has six ocelli, three on each side. The two lateral antennze form at 
about the same time, and have at first very much the same general appearance 
as the single median appendage. 
In the oldest larva (Figs. 3, 4) which I have studied all the cephalic ap- 
-pendages have grown more prominent, while the head itself has become con- 
siderably reduced in size. In addition to the median and lateral antenne, 
* The larval stages of Lepidonotus given above confirm closely in essential 
points the account of the metamorphosis of Polynoé contained in Max Miiller’s 
account published in Miiller’s Archiv for 1851. The segmentation and early de- 
velopment of the egg up to the formation of the monotrochal larva of an Annelid 
closely allied to Max Miiller’s Polynoé are figured by Sars (Wieg. Arch. 1845). 
t This larva was not raised from the former. 
