MOVEMENTS OF SARCODE. 149 



consist of extremely delicate protrusions of the wall or periplast of the 

 cell on which they rest, like the fingers of a glove"J each containing a 

 soft contractile sarcodous material (Kolliker) ; or, that they may be 

 gymnoplastic offshoots, that is, destitute of a distinct envelope. 

 Again, the longer duration of the movement after death, is only a 

 difference of degree; and this power endures longest in those animals 

 in which muscular contractility lasts longest. Finally, the discrepant 

 action of certain narcotics may be probably explained by future re- 

 searches. Admitting, however, the probability of the ciliary motion 

 being due to vital contractility, its rapid, rhythmic, concerted, and 

 maintained action yet remains to be explained. 



The use of the cilia in the respiratory organs of the higher air- 

 breathing animals, may be said chiefly to keep the membranes mo'st, 

 by distributing over them the secretion from their surfaces and fol- 

 licles ; and secondarily, by the definite direction of their motion, 

 which has been noticed invariably to be upwards towards the larynx, 

 to assist in raising and expelling the superabundant secretion upwards 

 from the air-passages. Their use in the ventricles of the brain, and 

 central cavity of the cord, is not known. On the gills of the young 

 Amphibia (tadpoles), and on the respiratory organs, whether laminated, 

 ramified, or sacculated, of the aquatic Mollusca and Molluscoida, they 

 appear to assist in the respiratory process, by keeping up rapid and 

 continuous currents over the respiratory surface, by which fresh por- 

 tions of fluid are continually brought into contact with it. In certain 

 cases (Ascidioida, Polyzoa), by creating currents, they also serve to 

 conduct alimentary substances into the opening leading into the 

 stomach, or the mouth, of the animal. As already mentioned, they 

 cause a rotatory movement of the embryos of certain vertebrate and 

 non-vertebrate aquatic animals. Finally, they constitute the proper 

 locomotive organs of the entire animal, in the Infusoria : in some of 

 these (Paramecium) the whole surface is ciliated ; sometimes, as in 

 Vorticella, there are a few ciliated fringes only around the mouth ; 

 and sometimes, as in the young Yorticellae, and in other species, there 

 is but a single long tail-like cilium, by the undulatory motion of which, 

 the microscopic being is propelled through the water in the opposite 

 direction. 



MOVEMENTS OF ANIMAL SARCODE AND PROTOPLASM. 



Movements, undoubtedly due to a vital contractility, take place, as 

 we have seen, in cells not possessed of the complex structure of mus- 

 cular fibre; such are the movements in the contractile cells of the 

 embryo heart of the Vertebrata, as in the chick or tadpole. In many 

 of the Annelida, and in other animals still lower in the scale, distinct 

 muscular fibres are replaced by an almost homogeneous tissue; the 

 cells of the Hydra, formerly believed to be themselves contractile, are 

 not now so regarded; but are considered as being rather of an elastic 

 nature, having contractile tissue lying between them. Still simpler 

 examples of sarcodous contractile movements occur in the gymno- 

 plastic white corpuscles of the blood, and in the so-called unicellular 



