18 PHYSIOLOGICAL SERIES. 



CEPHALOPODA. 



A. 59. The separate cartilages of a Cuttlefish (Sepia filHouxi). 

 The equatorial cartilage is peculiar in consisting of large 

 cylindrical cells, mostly arranged in a single layer, and 

 without processes ; its matrix is small in quantity and 

 forms a definite layer around each cell. In the other 

 cartilages the cells are small and more or less connected 

 by branched processes ; the matrix is very abundant and 

 structureless. It contains 1'22 % of chitin. 



Boll, Arch. f.Mikr. Anat., Bd. v. supplement, 1869, p. 14. 



Halliburton, Q. J. Micr. Sci., vol. xxv. 1885, p. 174. 



A. 59 a. A Cuttlefish (Sepia filliouxi) in which the natural 

 position of the cartilages is shown by the entire removal of 

 the soft parts on the left side. 



A. 59 b. A transverse section of the gill of a Cuttlefish (Sepia 

 officinalis), comprising four gill-lamella*. The lamelke 

 have been removed on the right to show a delicate rod of 

 cartilage that stiffens the free border of the supporting 

 membrane of each. 



A. 59 c. The cartilaginous skeleton of Nautilus pompilius. 

 When in its natural position the cartilage lies close behind 

 the buccal mass, sloping from above downwards and 

 forwards. The upper horns with their processes support 

 the central nervous system, the ventral flattened processes 

 are embedded in the sides, and the median in the roof, 

 of the funnel. In structure the cartilage corresponds to 

 that of Sepia. 



CEPHALOCHORDA. 



A. 60. The endoskeleton of Amphioxus lanceolatus. The skeleton 

 comprises a notochord, buccal cartilages, and a dorsal and 

 ventral row of fin-supports. 



The notochord extends from in front of the central 

 nervous system to the tip of the tail, and consists of a soft 

 core surrounded by a double sheath. The core is composed 

 of a series of transversely striated plates (possibly the walls 

 of extremely flattened chordal cells) arranged at right 



