288 SANTE NACCARATI 



other vertebrates, including man. It presents externally a 

 fibrous connective-tissue capsule in which, here and there, are 

 scattered pigmented cells (chromatophores) . From this capsule 

 issue numerous connective-tissue septa, which, gathering on the 

 inside of the gland, form a network enclosing the vesicles. These 

 vesicles, called also f olhcles or alveoli, are irregularly rounded, from 

 50 ju to 300 fj. in size, and are lined with simple epithelium, the 

 cells of which are mainly cubical, less often cyhndrical or flat, 

 and are in direct contact with the interior of the vesicular cavity, 

 in which is contained the colloidal fluid, an amorphous, homo- 

 geneous substance presenting under the microscope transverse 

 streaks or fissures and staining with acid stains; for example, 

 it stains pink with haematoxylin-eosin and yellow with Van 

 Gieson or with safranin and picric acid. The interior surface of 

 the epithelial cells, namely, the surface looking in the lumen of 

 the vesicles, is not clearly defined, but it has a broken appearance, 

 recalling that of the colloidal substance, and probably, since it is 

 not constant, due to the latter's remaining adherent to the cells. 

 The protoplasm is homogeneous and contains fine grains. The 

 nucleus always occupies the basal part of the cell, is well 

 marked, vesicular, rather large, and provided with chromatin 

 granules and does not have a nucleolus. The limits between the 

 cells are quite clear, and in the cellular walls, which are in eon- 

 tact with the connective tissue limiting the alveoli, there is a 

 basal membrane, not always, however, well differentiated. In 

 specimens colored with safranin and picric acid there are cells 

 having a nucleus which contains granules colored red (chromatin) 

 noticeable against the brighter background of the rest of the 

 nucleus, and cells whose nucleus is entirely colored red (fig. 3). 

 These two kinds of cells correspond to the two t;yT5es, principal 

 and colloidal, described by Langendorff, who interpreted them 

 as different aspects assumed by the same cell at different func- 

 tipnal periods. This interpretation seems very probable because 

 the aspect and the disposition of the cells in the diiTerent alveoli 

 is so variable that they suggest many functional phases from 

 the beginning elaboration to the complete secretion of the colloid. 



