180 BULLETIN OF THE 



The body of the youngest PhyllochcpAoptenis is divided into a large thick 

 anterior, and a smaller posterior region. The mouth opens as a triangular slit 

 on the ventral side, near the anterior extremity of the former. The posterior 

 extremity of the posterior region of the body bears a short median appendage. 

 The mesial band of cilia thus separates the body of the larva into two regions. 

 The anterior of these, which lies in advance when the Annelid is in motion, has 

 a slight depression in its ventral region which marks the position of the " gland- 

 ular body " described in the larva of Telcpsavus (and Spiocluetopterus). The 

 oesophagus, stomacli, and intestine can easily be seen through the walls of the 

 body. The anus opens on the dorsal side of the posterior body region, just in 

 advance of the medial caudal appendage. A still older larva (Fig. 18) shows 

 one in which two rows of cilia, separated from each other by a broad segment, 

 are well developed. A segmentation of that part of the posterior body region 

 which is behind the smaller ring of cilia, as well as the more elongated form of 

 the whole larva, is to be noticed in this worm. No cephalic tentacles have yet 

 formed, and the external surface of the body is still covered with small cilia. 

 The globular appendage to the posterior region of the body, figured by Clapa- 

 rede and Metschnikoff,* was not observed. The discovery of the youngest ot 

 these two larvae of Phyllochcetopterus is interesting, as showing how close the 

 resemblance between the youngest known Plnjlloclicetopterus] and the so-called 

 Tclepsavus larva is ; or, that the young Phyllochcetopterus larva has but one ring 

 of cilia between the anterior and posterior openings of the digestive canal, as 

 other mesotrochal larvae. The second and smaller ring is a later addition. 



Nephthys sp. 



Plate IV. 



The very little which is known of the development of NcjMiys we owe for 

 the most part to Claparede and Metschnikoff.:]: Larvse similar to those which 

 they describe, yet in different stages of growth, were raised or fished up in great 

 numbers in our work. 



The youngest of these (Fig. 1) are telotrochal, and may be classed with the 

 larva of Pohjcjorclius. The prajoral lobe is very large, and imparts an almost 

 spherical shape to the upper hemisphere of the larva. Equatorially about the 

 larva there runs a ridge upon which a circle of large and powerful cilia is 

 borne. The upper hemisphere or prteoral lobe is roimded ; the lower more 

 pointed. The whole larva has a green color, is somewhat transparent, and is 



both Telepsavus and Phyllochmtopterus, by Claparede and Metschnikoff, and in the 

 present paper. 



* Op. cit. 



t The adult Phyllochcetopterus has not been recorded in our waters. (See Verrill's 

 Check List.) Cliaparede and MetschnikofE's identification of the larva has been 

 followed in my studies. 



t Op. cit. 



