LINEUS. 261 



preservation appear in section as small pits (PL I., fig. 1). 

 Opening near them are the so-called head glands, which 

 in Lineus gesserensis form a small mass of gland cells 

 lying in the anterior portion of the snout just above the 

 rhynchodseum. 



(3) The eyes vary in number, the adult animal usually 

 having a dorso-lateral row of about five on each side. 

 They lie imbedded in the tissue of the snout well below 

 the epidermis and dorsal to the head slits. Each eye 

 consists of a deep layer of cells containing a dark brown 

 pigment, over which is a layer of pyriform cells (PL III., 

 fig 4), whose more pointed ends are drawn out into long 

 processes which are inserted into a fine nucleated mem- 

 brane. On the long processes of these ganglion (?) cells 

 may often be seen minute deeply-staining bodies, whilst 

 between them is a clear fluid kept in by the fine limiting 

 membrane and forming a lens. The eyes are supplied 

 by some of the cephalic nerves which enter them from 

 the pigmented side. Instances may frequently be 

 observed in which two eyes are incompletely separated, 

 whence it may probably be inferred that their number is 

 augmented by division of those already existing. The 

 young Lineus when hatched has but a single eye on either 

 side. 



THE CONNECTIVE TISSUES. 



These have been studied in the present species by 

 Montgomery (loc. cit. p. 1), who distinguishes the follow- 

 ing kinds : — 



(1) Branched connective tissue cells with inter-cellular 

 substance, composing the basement membrane of the 

 external epithelium, the outer and inner neurilemma, the 

 sheaths around the muscular fibres, the layer immediately 

 surrounding the intestine, the layer outside the endothe- 



