62 



CONNECTIVE TISSUES EPITHELIUM. 



ramifications of the bronchial tubes ; in the upper part of the vagina, the 

 uterus, and the Fallopian tubes ; and lastly, on the choroid plexus of the 

 lateral ventricles. In some vertebrata they also exist near the commence- 

 ment of the urinary tubuli. The cause of the movement is unknown ; it is 

 remarkable that it should persist long after the general death of the body. 

 A very peculiar form of cell, termed Cup, or Goblet-Cell (Fig. 

 18), appears scattered over parts that are usually covered by 

 columnar and ciliated cells. According to Klein, 1 they are 

 only the empty shells of the ordinary ciliated cells. In cer- 

 tain parts of the body as in the choroid coat of the eye, the 

 lungs and bronchial glands, and in the deep or Malpighian 

 layer of the epidermis of the negro cells are found loaded 

 with black pigment or melanin. The shape of these cells 

 varies from the most regular hexagonal to extremely irreg- 

 ular branched and caudate forms. They usually possess a 

 Cup or Gob- distinct nucleus, and the melanin is scattered through the 

 let-Ceil. otherwise clear protoplasmic cell-contents in the form of minute 

 granules. Some pigment cells, as those in the skin of the 

 Frog, 2 are capable of undergoing remarkable changes in their form and in 

 the distribution of the pigment-granules in their interior. They may con- 

 tract into spheroids, or may expand into a stellate form, with numerous 

 irregular, branched, anastomosing, and gradually attenuating processes; 

 and the pigment-granules may either accumulate around the central nu- 

 cleus, or be distributed through the protoplasm. According to Lister, their 



FIG. 10. 



FIG. 20. 



FIG. 21. 



Cells from Pignientum Ni- 

 gruni : a, pigmentary gran- 

 ules concealing the nucleus ; 

 b, the nucleus distinct. 



Various forms of Ciliated Epithelial Cells from 

 tin: trachea of a cat. 



Pigment-Cells from tail of Tadpole: 

 a, it, simple forms of recent origin ; 

 ft, ft, more complex, forms subse- 

 quently assumed. 



concentration follows exposure to the action of light, section of the nerve, 

 and the death of the animal. On the other hand, the molecules diffuse 

 themselves through the eel I -processes, when the animal is kept in darkness, 

 and when the skin is irritated. Heriug and Hoyer think the movements of 



1 Handbook- for the Physiological Laboratory, 1N73, p. 23. 



2 Sec tlic paper of Lister, in I'hil. Trans., 1858; ut' MM. iiering and Hoyer, in the 

 (Vmralblatt, 18G9, p. 49. 



