E NTozo A. ENTO ZOA. Entozoa. 



S03 



or four times, or even more. The anterior extremity 

 is, in general, marked by several black specks arranged 

 on each side of it, but variable in number. These are 

 considered to be the eyes. The mouth is anterior, and 

 almost always terminal, in the form of a slit, and for 

 the most part provided with a protrusile, long proboscis. 

 The intestine is simple, descending down the centre of 

 the body in a straight or undulating line to the oppo- 

 site extremity, where it opens outwardly by a pore 

 similar to the mouth. The sexes are separate, and 

 they multiply by ova, or perhaps, also, by transverse 

 sections. The species are all marine, and are found 

 living under stones and in mud between tide-marks. 

 They appear to dislike the light, and prefer to live in 

 obscurity. The species are very tenacious of life ; 

 if cut into several pieces, each lives and moves, and 

 perhaps each in time will grow up to a complete and 



perfect worm. Fresh water is a powerful poison to 

 these worms ; if placed in a vessel of this fluid, they 

 instantly show by their violent contortions how p;iiu- 

 ful and deleterious it is to them ; they soon break into 

 pieces, disgorge portions of their viscera, and .speedily 

 die and dissolve into a soft jelly. Some species pro- 

 gress like the leeches, moving in great undulations from 

 side to side, from right to left. All of them can creep 

 up solid plane surfaces by means of contractions which 

 sometimes change their general form in a very sin- 

 gular manner. The number of males appears to be 

 much inferior in proportion to that of females. As 

 Quatrefages remarks, this is the case also with many 

 of the intestinal worms ; in proportion, he says, as the 

 organization of the lower animals becomes degraded, 

 it appears that the female sex predominates mote 

 and more. 



Class— ENTOZOA (Intestinal Worms). 



As Siebold remarks, it is very diflioult to characterize 

 this class of worms, for it contains animals having 

 widely dissimilar organization. Indeed this is so much 

 the case, that some naturalists wish to suppress the 

 class altogether, and it has been attempted to divide 

 and isolate the orders amongst the various other classes 

 of the inferior invertebrated animals. But such vaiious 

 difiiculties have arisen from this, that in a work like 

 the present it is much better to keep the class as a 

 distinct one ; for if we fail to perceive any common 

 character in their organization, we can easily find one 

 ill their manner of living. The Entozoa are parasitical 

 worms, which either during their whole life, or at least 

 a part of it, inhabit the bodies of other animals, and 

 derive their nourishment from them. 



The nervous system is feebly developed, and has 

 only lately been distinctly recognized. In the majority 

 it consists of two ganglia or two pairs, which unite 

 together by a median band or narrow commissure, and 

 give origin to two long cords which nm through the 

 whole length of the body. In some no vascular 

 system has been recognized, but in others it is well 

 developed. The circvdating liquid, however, or blood, 

 is in general wholly colourless. The digestive organs 

 vary very much in the different orders. In some, as 

 the Cestoid inorms and the Acanthocephali, neither 

 mouth nor alimentary canal have been observed — 

 (Siehold) ; but in other orders it is pretty well developed. 

 No respiratory system has as yet been satisfactorily 

 observed. The intestinal worms, as their name im- 

 ports, are almost all inhabitants of the internal parts of 

 other animals ; there alone can they continue their 

 species, and there alone can they obtain their nourish- 

 ment. There is scarcely one animal that is exempt 

 from these parasites ; and in general each genus seems 

 to possess one or more species peculiar to itself, though 

 often several species infest the different cavities of the 

 same animal at the same time. For instance, there are 

 about twenty distinct species that are found either in 

 some of the cavities or in the muscular substance of 



man. They are most frequently met with in the 

 alimentary canal, but they occur also in the cellular 

 tissue, and in the parenchyma of the most closely- 

 invested viscera, such as the liver and the br.iin. 

 Though they are very frequent in diseased states of 

 the viscera, and, when numerous, are the cause of 

 disease themselves, they yet occur abundantly in per- 

 fectly healthy subjects. Most of the Entozoa propa- 

 gate by means of genital organs, which in some are 

 situated upon a single animal, and in others upon two 

 separate individuals. A few, however, multiply by 

 fissuration, as is the case in the Tape-worms {Ticida). 

 The old opinion, therefore, that intestinal worms were 

 products of spontaneous generation, is now completely 

 exploded. It is exceedingly difficult, however, to 

 conceive how these creatures can get into some of the 

 obscure and well protected organs and parts of the 

 body in which they are found. Not only the liver and 

 brain, as mentioned above, but the lungs and blood- 

 vessels are infested with them ; and it is affirmed they 

 even occur in the unborn fcetus. Some of the species, 

 too, attain a large size ; and we must conclude that 

 the germs from which they spring must be exceedingly 

 minute, as the)' must be capable of being transmitted 

 through capillary vessels and apertures too small to be 

 discerned by the naked eye. 



The Entozoa dill'er very much from one another in 

 form and organization, and, according to Cuvier and 

 Professor Owen, have been divided into two large 

 orders — I. Nematoid or Cavitary Entozoa (=Coelel- 

 mintha — Owen) ; those which have an intestine float- 

 ing in a distinct abdominal cavity, commencing with a 

 mouth, and terminating with a vent; II. Parenchy- 

 matous Entozoa (=Sterelmintha — Owen) ; those which 

 have the viscera obscure, generally in the form of vas- 

 cular ramifications, or even not discernible at all. By 

 this arrangement, however, worms the most dissimilar 

 in their general appearance arc grouped together, and 

 a more natural method has been generally adopted. 

 Rudulphi divides them into five orders, basing his 



