1883.] 



MICROSCOPICAL JOURNAL. 



71 



General Appearance, etc., of Vi- 

 BRATiLE Cilia. — The dififerentiation 

 of vibratile cilia takes place only in 

 the superficial layers of protoplasm, 

 or in the superficial layers of cells of 

 some epithelial tissues. Thus, in the 

 protozoa, the cilia are attached di- 

 rectly to the tissues of which they 

 form a part, while in all the higher 

 orders we find unmistakable evidence 

 of an epithelium. In most cases the 

 cilia are arranged in regular order, — 

 in circles, spirals (in many infusoria), 

 or in straight rows (gills of mussels 

 and other epithelia); they usually 

 stand erect, and at right angles to the 

 surface on which they are situated. 

 They are transparent and homogene- 

 ous throughout, and for the most part 

 colorless, though in some instances 

 (sea mussels e.g.) a slight brown or 

 yellowish-brown tint has been ob- 

 served. Their usual transparency and 

 lack of color has been the cause of 

 their presence being overlooked in 

 many cases, the difficulty of seeing 

 them while in motion being well 

 shown by the endeavors of Messrs. 

 Dallinger and Drysdale to demon- 

 strate the presence of cilia in Bactcr- 

 iutn tcnno. 



Cilia are, as a rule, firm, pliable, 

 and elastic, and in the infusoria and 

 other invertebrates may sometimes 

 be split up into bundles of finest 

 hairs, by means of pressure or chemi- 

 cals. They are doubly refractive, and 

 uniaxal, the optical axis in all cases 

 coinciding with the direction of great- 

 est length. In form they may vary 

 somewhat, but are generally slender, 

 conical or flattened filaments, broad 

 at the base or root and tapering 

 gradually to the point. Ehrenberg 

 describes compound cilia in the infu- 

 soria. In ciliograde medusae the 

 cilia are broad, flattened organs, each 

 of which is made up of several single 

 filaments, joined together throughout 

 their whole length by a connecting 

 membrane presenting the appearance 

 of an undulating, homogeneous mem- 

 brane, which may also be observed 

 in the seminal filaments of the sala- 



mander, triton, bombinator, and in 

 many infusoria; while leaf-shaped 

 cilia are to be seen»in some inverte- 

 brates. 



In all ciliated epithelial cells of 

 higher animals, and in most of the 

 spermatozoa of animals and plants, 

 the shape is as first described, i.e.., 

 small, slender, conical hairs. As to 

 size, vibratile cilia may difi"er even in 

 the same cell, as well as in different 

 parts of the same animal and in dif- 

 ferent animals. Their thickness is 

 scarcely measurable, but in length 

 they range from the unparalleled un- 

 dulating hairs of the infusorial para- 

 site Trichonympha agilis, Leidy, to 

 the minute cilia of the human trachea 

 (0.003 ^o 0.005 mm).* They have 

 been observed to be longest in ma- 

 rine animals and spermatozoids. 



The number of cilia implanted 

 upon one cell in ciliated epithelium in 

 vertebrates, ranges from ten to thirty, 

 but we find exceptions to this rule, as 

 in the instance already noted of the 

 cells of the uriniferous tubes of the 

 serpent, which have but one. The 

 presence of a single, usually very long, 

 hair is frequently met with in the 

 epithelial cells of invertebrates t as 

 well as in spermatozoids, protozoa, 

 and algae. Such cells are termed 

 flagelliform cells, in contradistinction 

 to ciliated cells proper ; while those 

 unicellular organisms provided in this 

 manner are separated from ciliate in- 

 fusoria in general, under the name 

 flagellata. 



The shape and size of the cells to 

 which cilia are attached are not con- 

 sidered characteristic. They are often 

 cylindrical, often flat or squamous, 

 and always contain a spherical or oval 

 nucleus which may conceal one or 



* Human Epididymis 0.022 to 0.034 mm. 

 Coni vasculnsi 0.0114 mm., Branchial laminae 

 of Buccinatum iindatum 1-500 inch, Swimming 

 organs of Ctenophora I mm. Organ of 

 Jacobson in Rabbit 0.0054 mm. 



t In Flttstra carbesia Dr. Grant estimates 

 the number of cilia upon a moderate sized 

 animal as forty millions, — about fifty on each 

 side of a tenaculum. 



