MUSEUM OF COMPAKATIVE 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 i- 

 not ])erfectly equatorial. The pole of the cephalic hemisphere is pointed, an^l 

 bears two eye-spots connected over the dorsal surface of the prseoral 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, oesophagus, and intestine, 

 which are not clearly differentiated from each other. 



The next oldest larva (Figs. 16, 17), Lejpidonotus, is characteristic.f 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, «). Upon the back of the larva we find rudiments of the 

 elytra as diminutive circular plates hangmg from the bases of the parapodia, 

 which, however, do not cover these bodies. The interior of the larva is taken 

 up by an oesophagus, a large stomach, which fills most of the prsoral 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. (PI. 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. Tlie 

 larva now has six ocelli, three on each side. The two lateral antennae 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 antennae, 



* The larval stages of Lepidonotus given above confirm closely in essential 

 points the account of the metamorphosis of Pol/jnoe contained in Max MuUer'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 Polynoe are figured by Sars (Wieg. Arch. 184o). 



t This larva was not raised from the former. 



