ENTOZOA. 43 



There arc few common and positive organic characters which can 

 be attributed to this very extensive and singular group of animals : 

 they have generally a soft, mucous and colourless integument, which in 

 a few species is armed with spines. That the integument should be, 

 uniformly white or whitish might, a pi'iori, have been expected of 

 animals which are developed and exist in the dark recesses of other 

 animal bodies. The mature ova are almost the only parts which 

 naturally acquire a distinct colour ; and the subtransparent body some- 

 times derives other tints from the accidental colour of the food. Ex- 

 cluded also by the nature of their abode from the immediate influence 

 of the atmosphere, no distinct respiratory organ could be expected to 

 be developed in the Entozoa; but this negative character is common to 

 the Entozoa with most of the other Radiata of Cuvier. In creatures 

 surrounded by and having every part of their absorbent surface in con- 

 tact with the secreted and vitalised juices of higher animals, one might 

 likewise have anticipated little comj^lexity and less variety of organ- 

 isation. Yet the workmanship of the Divine Artificer is sufficiently 

 complicated and marvellous in these outcasts, as they may be termed, 

 of the Animal Kingdom, to exhaust the utmost skill and patience of 

 the anatomist in unravelling their structure, and the greatest acumen 

 and judgment in the physiologist in determining the functions and 

 analogies of the structures so discovered. What also is very re- 

 markable, the gradations of organisation that are traceable in these 

 internal parasites reach extremes as remote, and connect them by 

 links as diversified, as in any of the other groups of Zoophyta, although 

 these play their parts in the open and diversified field of Nature. 



Beginning with the lowest link we have to commence with a con- 

 dition of organisation more simple than is presented by the lowest 

 Infusory or Polype. We end with a grade of organisation, which, 

 whether it is to be referred to the radiated or articulated types, 

 zoologists and anatomists are not yet unanimous. 



Amongst the vermiform animals with colourless integument, co- 

 lourless circulating juices and without respiratory organs, two leading 

 differences of the digestive system have been recognised : in the one 

 it is a tube with two apertures contained in a distinct abdominal 

 cavity ; in the other it is excavated or imbedded in the common 

 parenchyme of the body, and has no anal outlet. The first condition 

 characterises the Vers Intestinaux Cavitaires of Cuvier ; the second 

 the Veis Intestinaux Parenchymateux oi the same naturalist, 



I have rendered the Cuvierian definitions of the two leading 

 classes or groups of the Entozoa by the names '* Coelelmintha," and 

 " Sterelmintha." 



