70 



THE AMERICAN MONTHLY 



[April. 



all fields for the study of vibratile 

 cilia, viz., the infusoria. At first as 

 he noticed in the- water the wonderful 

 little forms he imagined, as Cohn tells 

 us, that he saw the living atoms 

 which, according to Democritus com- 

 posed all bodies, and from whose 

 whirling motion hiscontemporar)- Des- 

 cartes believed the world "built itself 

 anew." However, he soon became 

 convinced that these were animalcu- 

 les and accounted for their motion by 

 the cilia, which he described. In 

 1683 Ant. de Heide, a Dutch physi- 

 cian, noticed the presence of vibratile 

 cilia upon the branchial membranes 

 of the common horse-mussel {Modiola 

 modiolus) the movement of which he 

 described as " motus radiosiis " or 

 " tremu/us." 



These discoveries having created 

 some interest in the phenomena pre- 

 sented by vibratile cilia, they were 

 shown, in the latter part of the last 

 and the early part of the present cen- 

 tury, to exist in the most widely sepa- 

 rated members of the animal kingdom. 

 The first connected examination and 

 descriptions were given by Purkinje 

 and Valentin, and a little later by, 

 Sharpey. In regard to the more im- 

 portant works which have since ap- 

 peared, we will make reference in 

 various places.* Steinbuch was first 

 to discover the movement in ver- 

 tebrates (tadpole and larvae of sala- 

 mander) while Dr. Grant was the first 

 to demonstrate the existence of cilia 

 as organs by which motion within the 

 ovum is produced. He, however, 

 seems not to have appreciated their 

 respiiatory significance. 



Distribution of Vibratile Cilia 

 Among Animals. — Vibratile cilia are 

 found very generally distributed 

 throughout the animal kingdom. One 

 class only, the articulata, is without 

 them, unless we accept the classifica- 

 tion of some naturalists and include 



*It would l)e impossible to make complete 

 references to the extensive literature on tlie 

 appearances and structure of ciliated cells 

 among the invertebrates. 



the rotatoria within this group, under 

 the head of Cilio-articulates.* With 

 the exceptions named, vibratile cilia 

 are constantly found from the lowest 

 to the highest grades of animal life, 

 differing only in manner of arrange- i 

 ment, and existing, as a rule, on sur- I 

 faces exposed to fluids or producing 

 fluid secretions. 



The unicellular protozoa (flagellata J 

 and ciliated infusoria) are signalized ' 

 by a wonderful manifestation of ciliary 

 organs, while the multicellular organ- 

 isms, from sponges up to man, show 

 the presence of vibratile cilia attached 

 to epithelial cells, which, for the most 

 part, are grouped together to form 

 wide expansions of ciliated epithelium. 



Animal spermatozoids are only 

 modified ciliated, epithelial cells, in 

 which the difi^erentiation has produced 

 but one cilium, the cell at a certain 

 period of its career becoming motile. f 

 The life-conditions of the spermatozoa 

 are really the same as those of ciliary 

 motion in general, and the movement 

 of the appendage of the zoosperm is 

 exactly analogous to that of the cilium 

 of Bacterium tcnno. 



The presence of but one cilium is 

 not anomalous among ciliated epithe- 

 lial cells, and is by no means confined 

 to spermatozoa, it having been noted, 

 for instance, in Sponges and Hydroid 

 polyps and in the winding urethral 

 canal of the serpent, and in the audi- 

 tory organs of the cyclostomum.J 



*The Crustacea ])ossess the auditory cells 

 with stiff cilia; also spermatozoids, with a 

 number of appendages. These ciliary ravs 

 may be withdrawn and the seminal element 

 assume a spherical form. 



t '' According to Schvveigger-Seidel the 

 seminal element is not simply a modified nu- 

 cleus, but corresponds to an entire cell, as a 

 metamorphosed singlv-ciliated cell." Pfliiger 

 describes the seminal element as a small 

 ciliated cell and attributes its formation to 

 free-cell formation. 



t On the other hand we see the seminal 

 filaments of the tardigrade arachnida pos- 

 sessed of two terminal vibrating tails, and 

 those of FaluduKi viripara having a tuft of 

 short cilia springing from their thicker ends 

 (Leydig). 



