CEPHALOPODA. 1 9 1 



faintly and presents the appearance of a number of delicate fibrils twisting about in 

 all directions and leaving spaces in which nuclei are situated, though no definite cell 

 boundaries can be distinguished (fig. 4. cm.). The nuclei measure about 0*0058 millim. 



in diameter, and nucleoli can be seen in them. This central mass rises as a founded 

 lump to a height of about 0'18 millim. 



The greater part of the centre of the stem is made up of a peculiar radially 

 arranged supporting tissue, which stains very deeply with hematoxylin. In sections 

 near the base of the papilla this tissue appears as a ring around the central mass and 

 consists of very thin radiating fibres (Plate III., figs. 1 to 4, /.). which are collected 

 together in masses forming little trabecular, which arise from the surface of the central 

 mass and pass outwards, slightly diverging from each other and leaving clear spaces 

 between them. The rounded spaces at the outer ends of the trabecular are occupied 

 by bundles of fibres, which run parallel with the axis of the stem : transverse sections 

 of these bundles are seen in fig. 4, h. The trabecular stain a deep purple with 

 hematoxylin, and thus are in marked contrast with the central mass. They present 

 a number of ovoid nuclei intercalated here and there among the fibres. Above the 

 central mass this axial structure occupies the centre of the stem (compare figs. 1 and 

 2), and rises up to a height of about 07 millim., when it gradually merges into the 

 other tissues of the stem. This axial supporting tissue is produced into the branches, 

 but here it has the appearance of irregular transverse septa (fig. 6, r.) with spaces 

 between. The septa are not separate, but continuous with the adjacent ones on 

 either side, owing to their curved form and to connecting pieces passing from one to 

 another. Towards the tip of the branches this tissue becomes less abundant and 

 merges into the surrounding connective-tissue. In the stem this axial tissue is seen 

 to be supplied with blood vessels (fig. 4, hi.), but I have not succeeded in detecting 

 any nerves in it. 



Around this central column is a layer ot connective-tissue (tigs. 1 to 3, c.) varying 

 from 0"05 millim. to 0*02 millim. in thickness. This is of a loose open nature, with 

 delicate fibrils and numerous large lacunar ; small ovate or spheroidal nuclei are 

 scattered in it here and there. This layer extends into the branches, in the larger of 

 which it is about - 03 millim. in thickness (fig. 5, a), and gradually disappears towards 

 the tips. Within this connective-tissue layer are the chromatophores and another 

 granular element to be described below. 



The chromatophores (eh.) are situated in the outer layers of this connective-tissue, 

 either immediately below the epithelium or not very far removed from it. They have 

 the form of little sacs, on an average about 0"035 millim. in diameter. Very often 

 there is a vacant space immediately below the chromatophores (figs. 4 and 13, I.). 

 Where the section passes tangentially through the wall of a chromatophore the 

 pigment is seen to be composed of minute granules (fig. 12, ch.). 



In the connective-tissue layer are also seen here and there masses of substance 

 staining of a paler and more reddish colour than the other tissues and of homogeneous 



