MUSCULAR SYSTEM. 



533 



We need scarcely say that in the Agastrica 

 no muscular system whatever can be detected, 

 the living portions of their bodies being entirely 

 made up of a soft granular parenchyma which 

 only dubiously exhibits contractile movements 

 under any circumstances. 



In the Polypipheru we find a very extensive 

 group of animals naturally allied to each other 

 in the general details of" their economy, but 

 offering very great diversity of structure and 

 external form. In the simplest or gelatinous 

 Polyps ( Hydrida ) the acrite condition of the 

 nervous and muscular tissues is most conspicu- 

 ously exemplified. Examined under the mi- 

 croscope, the entire substance of the minute 

 gelatinous bag composing the body of the 

 Hydra seems to consist of a glairy material, 

 wherein are suspended coloured globules that 

 constantly change their relative positions, and 

 move about from place to place as the creature 

 contracts, or extends different parts of its sub- 

 stance, but not a fibre or filament is discernible 

 passing in any direction, nevertheless the move- 

 ments of the Hydra appear to be performed 

 with facility, and its powers of locomotion are 

 considerable. 



In the Alcyonidse and other compound cor- 

 tical Polyps, muscles of any kind are equally 

 invisible, and the contractions observable either 

 in the substance of the common body or in the 

 numerous hydriform mouths that minister to 

 the support of the general mass, seem to be 

 entirely due to the approximation of molecules 

 diffused through the entire substance of the 

 animal, rather than dependent upon any thing 

 like muscular structure; nevertheless it has been 

 stated, though perhaps erroneously, that some 

 families (the Pennutulida) are able to swim 

 from place to place by consentaneous move- 

 ments of the polyps and polyp-bearing arms 

 with which many species are provided. 



The tubular Polyps are equally devoid of 

 any thing like muscular fibre, nevertheless the 

 soft and uncalcified membrane that connects 

 the Polyps to the cells wherein they are lodged, 

 and the Hydriform Polyps themselves, are en- 

 dowed with the capability of performing all the 

 movements required to protrude the flower-like 

 bodies from the cups that contain them, and to 

 seize and swallow the materials required for 

 their support. 



But in every group of animals, as we ap- 

 proach the most highly organized members of 

 that group, we find the characters of a more 

 exalted type of organization beginning to ma- 

 nifest themselves, and thus in the Actiniad<e, 

 which are obviously esculent between the 

 Acrite Polyps and animals possessing a true 

 muscular system, a fibrous arrangement of the 

 contracting portions of the body becomes very 

 distinctly recognisable, and a nervous filament 

 may be displayed under favourable circum- 

 stances passing round the oral extremity of the 

 creature, and thus closely approximating the 

 nematoneurose type of structure. The infuso- 

 rial animalcules ( Polygastrica, Ehren.) seem, as 

 far as relates to their muscular system at least, 

 to be strictly acrite animals, but such is their 

 extreme minuteness, that much uncertainty 



still necessarily exists concerning their intimate 

 organization. Their locomotive apparatus mo.st 

 frequently consists of fringes of vibratile cilia 

 variously disposed, the movements of which 

 are most probably dependent upon the exist- 

 ence of a peculiar vital tissue distinct from 

 muscle. In many species, e. g. the Proteus 

 (Amoeba diffluenx), the contractions of the 

 body are extensive, so that even the outward 

 form of the animalcule is perpetually changing, 

 and some, the Vorticella, are attached to highly 

 irritable pedicles of exquisite tenuity, that 

 may be straightened or suddenly thrown into 

 close spiral coils by some inherent power, the 

 nature of which is as yet quite incompre- 

 hensible. In some, as for instance Chilvdon 

 uncinatus, moveable hooks are found to be ap- 

 pended to the surface of the animalcule, and 

 some (Nassula) are provided with a peculiar 

 dental apparatus, consisting of a minute cylin- 

 der of horny filaments; nevertheless no appear- 

 ance of muscular or nervous fibre has as yet 

 been detected even in the largest and most 

 conspicuous species. 



The ACALEPHJE next claim our notice as 

 members of the Acrite division of the animal 

 creation, and in every point of their economy 

 they strictly conform to the general characters 

 belonging to this type of organization. (See 

 ACRITA.) Their bodies are soft, pellucid, and 

 gelatinous, without any trace of muscular fibre 

 being perceptible in their composition ; their 

 digestive canals are excavated in the paren- 

 chyma of the body, not contained in any abdo- 

 minal cavity, and the canals through which 

 nutrimentis conveyed todifferentpartsofthesys- 

 tem are entirely devoid of proper external coats ; 

 neither, as we believe, do nerves exist in any 

 of the class, although, as we are well aware, 

 two eminent observers have entertained a con- 

 trary opinion. Professor Grant,* in his account 

 of the anatomy of Cydippe pileus, describes a 

 double ring of nervous fibre as surroundiii- 

 one end of the alimentary canal of that beau- 

 tiful little Acaleph, and has even figured ganglia 

 distributed at intervals upon these circular 

 cords, from which secondary nerves are de- 

 scribed as emanating. Such a circumstance as 

 the existence of nerves and ganglia in an ani- 

 mal confessedly acrite, and presenting no traces 

 of that type of structure which, in all other 

 cases, invariably accompanies so elevated a 

 condition of the nervous system, from its very 

 singularity was well calculated to attract the 

 notice of the physiologist, and we are ourselves 

 quite satisfied that the distinguished professor 

 has been led into error upon this point, most 

 probably from having mistaken the circular 

 canals, described by Delle Chiaje and others, 

 as surrounding the oral extremity of the Beroes, 

 and which are indeed frequently filled with an 

 opaline fluid, for nervous fibre.f 



* Vide Transact, of the Zoological Society of 

 London, vol. i. and the figure at p. 109, vol. i. of 

 this work. 



t At the Birmingham meeting of the British 

 Association, during a very interesting discussion 

 upon this point, it was agreed by Mr. Forbes and 

 Mr. Thompson, whose qualifications for such re- 



