^16 Dr Gairdiiei's Analysts of 



to the liver of the higher animals, from their colour, form, and 



connexions. They must, however, be left to further inquiries. 



2. Muscular System. — A fibrous muscular tissue being the 

 proper agent of all voluntary contraction in the animal king- 

 dom ; we might, a priori, expect its existence in the class of 

 infusoria, which are so remarkable for the rapidity and energy 

 of their movements of propulsion and translation. In the for- 

 mer they can only be compared with fishes, and in the latter 

 with insects. Contractility of tissue can never explain those 

 active voluntary efforts by which they avoid obstacles when 

 swimming in myriads in a single drop, convey the nutriment to- 

 wards the mouth, and perform the act of deglutition. Previous, 

 however, to Dr Ehrenberg, nothing like the muscular fibre had 

 ever been attempted to be shewn in these animals. 



As yet, from their extreme tenuity, no distinct fibres have 

 been detected in the second and more minute division styled 

 by Cuvier Homogeneous Infusoria, and in the new system of 

 Dr Ehrenberg Polygastrica ; although from their extremely vi- 

 gorous contractions, as well as from their presence in the divi- 

 sion of the Rotatoria, we are entitled to infer their existence. 

 In this last, distinct fibres are perceptible in the Eosphora nqjas. 

 Rotifer vulgaris, Philodina erythrophthalma and Hydatina 

 senta. 



We shall select the muscular system of the latter, the Hyda- 

 tina senta, as a specimen, from its greater distinctness and com- 

 plexity. The perfectly transparent gelatinous body of this ani- 

 mal, when seen through the microscope with a power of 380, 

 appears to be traversed longitudinally by several narrow bands 

 of fibres, perfectly transparent, and of a greyish-white colour. 

 When the animal throws itself into its violent lateral contor- 

 tions, these fibrous bands are observed to shorten, become 

 broader and thicker (from their slightly diminished transpa- 

 rency), on the side towards which the contractions are made; 

 and on the convex to become so extremely elongated and at- 

 tenuated as to be almost, in some cases, quite imperceptible. 

 The real muscular nature of these organs, and that they are 

 the real agents in effecting the motions of the animal, is thus 

 placed beyond all doubt. These muscles never lose their appa- 



