3 o CHORDATE ORGANIZATION n.6- 



known whether this cuticle contains a substance similar to the keratin 

 produced by the many-layered skin of later forms. There are receptor 

 cells but no glands or chromatophores in the skin. 



Below the epidermis is a fibrous cutis, and below this again a 

 gelatinous material containing fibres, the sub-cutis. Both these layers 

 are secreted by scattered cells having some similarity to the fibroblasts 



Fig. 8. Anterior end of amphioxus, from a stained and cleared preparation 

 of a young animal. 



b.c. buccal cirri;/, fin-ray box; II. p. Hatschek's pit; my. myotome; n. notochord; 

 n.c. nerve-cord; p. pigment spot; ph. pharynx; v. velar tentacles; zi.o. wheel organ. 



of higher forms. They contain a system of cutaneous canals, with 

 endothelial lining (Fig. 14). 



7. Mouth and pharynx and the control of feeding 



Amphioxus obtains its food by extracting small particles from a 

 stream of water, which it draws in by means of cilia. In all animals 

 that use cilia for this purpose a very large surface is provided (e.g. 

 lamellibranchs, ascidians), and the pharynx and gill bars of amphioxus 

 occupy more than one-half of the whole surface area of the body. 

 Special arrangements are made for the support and protection of this 

 ciliated surface, the wall of the pharynx being so greatly subdivided 

 that it needs the protection of an outer layer, the atrium. 



The mouth lies covered by an oral hood whose edges are drawn out 

 into buccal cirri, provided with sense-cells (Fig. 8). When feeding the 

 cirri are curved to form a funnel-like sieve preventing the entry of 

 large particles. Around the mouth itself there is a further ring of 



