ON LAEViE OF LINGULA AND PELAGODISCUS (DISCINISCA). 63 



are hollow, and the comparatively large cavity, which opens into the arm-sinus, is 

 lined by an epithelium and contains longitudinal muscle-bands. The cells on the 

 medial face of each cirrus bear long cilia. As in Lingula, the deeply staining 

 epithelium of the cirri is thrown into annular folds by contraction of the muscles. 

 Supporting substance is not recognisable in sections of the cirri, but is present in 

 each half of the lophophore as a narrow band lateral to the arm-sinus, and extending 

 along the region of attachment of the cirri. The greater part of each cirrus, the 

 distal region of the tentacle and the ciliated tracts, right and left, in its basal 

 portion were yellow in life. There was also a considerable amount of yellow 

 pigment in the lip which overhangs the mouth in front, and a narrow transverse 

 band of brownish pigment in the ventral body- wall immediately anterior to the 

 sub-oesophageal ganglion. 



There is a deep depression on the ventral side between the posterior margin of 

 the lophophore and the anterior edge of the wall of the body proper (fig. 17). In 

 this depression, and situated on the anterior surface of the wall of the body proper, 

 just ventral to the oesophagus, is the large ventral nerve-ganglion. The two lateral 

 ganglia, which are also large, are situated in the body-wall in front of the anterior 

 margins of the occlusors.* 



The outline of the wall of the body proper is almost semicircular or bluntly 

 conical, its form and height depending on the condition of expansion or contraction 

 of the animal. In the lateral wall of the body proper, rather nearer the dorsal 

 than the ventral surface, is on each side a large black, or brownish-black, oval 

 pigment-spot or " eye," about 20ju, long. Similar pigment-spots were present in the 

 larvae examined by Fritz Muller, but not in those described by Drs Blochmann 

 and Yatsu. 



The epidermis of the body- wall in the region of the " eye," especially ventral and 

 posterior to it, is higher than elsewhere, and forms a regular columnar epithelium. 

 This elevation, which is readily seen in most specimens mounted whole, probably 

 represents a sensory area. 



The "eye" is like a shallow cup in shape (fig. 18), and consists of masses of 

 brown pigment-spherules deposited in the distal ends of several of the epithelial 

 cells. Immediately below the epithelium of this region of the body-wall is a nervous 

 tract extending backwards from the lateral ganglion, which supplies the columnar 

 epithelium described above, the " eye," and the statocyst. 



In the dorsal body-wall on each side is a large statocyst situated immediately 

 posterior and slightly lateral to the dorsal margin of the massive anterior occlusor 

 muscle (fig. 12). The maximum internal diameter of the statocyst is about 25/u, ; 

 the external diameters are : antero-posterior, 30-40/x, ; transverse, 25-30/a ; dorso- 

 ventral, 10-15/a. In surface view the statocyst is ovoid, and the narrower end, 



* That is, the anterior occlusors ; there are no posterior occlusors at this stage. Professor Blochmann has given 

 an account of the muscles of the larva, to which I have nothing special to add. 



