1-12 Prof. H. N. Moseley on the 



mentum), and never being present on the girdle or zona, 

 which is occupied, as is well known, by various calcareous 

 structures, some of which have been carefully investigated by 

 Reincke *. 



In the case of all the intermediate shells the eyes are con- 

 fined to the areas laterales, or to the line of demarcation 

 between the area? laterales and the area ventralis, which latter 

 is usually entirely devoid of them. 



The eyes, which are mostly circular in outline as seen on 

 the shell-surfaces, measure about yt7> of an inch in diameter 

 in Scht'zocJnton incisus, -g}^ of an inch m Acantliopleura spini- 

 gera^ and in CorepMum aculeatum (in which they are oval in 

 outline) ^^ of an inch by about i^^. In Enoplocliiton they 

 are smaller still and only with difficulty seen at all. 



The eyes appear, when viewed by reflected light with a 

 low powSr of the microscope, as highly refracting, convex, 

 circular spots, looking as if made of glass or crystal ; they 

 are surrounded and set off by a narrow zone of dark pigment, 

 which is the margin of the choroid seen through the superficial 

 shell-substance. In the centre of each convex spot is a 

 smaller circular area, somewhat darker, caused by the outline 

 of the iris, but showing a brilliant speck of totally reflected 

 light, due to the lens. 



The entire substance of the tegmentum in the Chitonidffi 

 is traversed by a series of branching canals, which are occu- 

 pied in the living condition of the animal by corresponding 

 ramifications of soft tissues, accompanied by abundance of 

 nerves. The nerves and strands of other soft tissue enter the 

 substance of the tegmentum along the line of junction of its 

 margin with the upper surface of the articulamentum. A 

 narrow area, perforated all over by pores, so as to have a 

 sieve-like appearance, here intervenes between the two com- 

 ponents of the shells, and in some shells the actual margin of 

 the tegmentum itself is perforated. In the case of the inter- 

 mediate shells, in most genei'a there are a pair of slits (incisuras 

 laterales) , one on either side, in the lateral lamina of insertion ; 

 these slits lead to two narrow tracts in the deeper substance 

 of the shell, which follow the line of separation between the 

 area centralis and the areas laterales of the tegmentum. These 

 narrow tracts are permeated by numerous longitudinal canals 

 which lodge each a specially large stem of soft tissue and 

 nerves, which ramifies in the substance of the tegmentum. 

 Corresponding with this tract on the under surface of the shell 

 are a series of minute openings leading into it, through which 

 further strands of soft tissue, possibly mostly nervous, pass 



• " Beitrjige zur Bildimgsgescliiclite der Staclielu &c. im ^lantclrandc 

 der Ohitoneii," Zeitschr. fiir wi.'^s. Zool. Bd. xvii. S. 305. 



