ENTOZOA. 



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ENTOZOA. 



1. E. ericetorum, C. Miill. = Gymnosto- 

 mum fascicular e, Hook, and Tayl. 



2. E. Templetoni, Schwagr. = Weissia 

 Templetoni, Hook, and Tayl. 



ENTOZOA.— A class of Animals. 



The Entozoa are animals residing para- 

 sitically, during either the whole, or a part of 

 their lives, in the cavities or in the substance 

 of the organs of other animals; they are 

 very generally met with throughout the 

 Animal Kingdom; and they derive their 

 nourishment from the liquids of those ani- 

 mals of which they constitute the parasites. 

 Their form is mostly elongate, and the body 

 more or less distinctly jointed. 



The integument consists of a delicate ho- 

 mogeneous epidermis, often thrown into 

 numerous transverse folds ; sometimes also 

 into longitudinal folds, giving the body a 

 winged appearance. In some species, it is 

 furnished with papillae, spines, or horny 

 reflexed prickles, either scattered over the 

 greater part of the surface, or confined to the 

 anterior extremity of the body ; in the latter 

 case serving as organs of adhesion. Beneath 

 the epidermis is the cutis, intimately fused 

 with, or almost entirely consisting of layers 

 of transverse, longitudinal and oblique flat- 

 tened fusiform muscular fibres, resembling 

 the organic or un striped muscular fibres 

 of the Vertebrata. 



Beneath, or in the substance of the skin, 

 the Cestoid Entozoa, are numerous 



in 



minute oval or rounded bodies, containing 

 carbonate and phosphate of lime ; these are 

 regarded as forming the rudiments of a cuta- 

 neous skeleton, and they possess a concentric 

 laminated structure. 



The form and structure of the head and its 

 appendages, in the shape of hooks, suckers, 

 &c., are described with the genera and 

 species, as their form and arrangement are 

 used as generic characters. 



The nervous system of the Entozoa is not 

 well known. In the cystic or larval forms, 

 none has been detected. In the Cestoids 

 and Acanthocephala, it appears to consist of 

 a single cephalic ganglion, sending ofl^ 

 branches to the proboscis. In the Trema- 

 toda, of two oesophageal ganglia, connected 

 by a transverse chord, and sending off two 

 lateral branches, which traverse the body 

 longitudinally. In the Nematoidea, it is 

 composed of a single longitudinal cord, fur- 

 nished at its origin and termination with a 

 ganglion. 



Organs of special sense appear to be 

 absent in the Entozoa, excluding that of 



touch, which resides in the various cephalic 

 appendages. In some, especially in the 

 ciliated embrjonic form, there are red or 

 black cervical spots,which have beenregarded 

 as eyes ; but they do not appear to contain 

 any refracting body comparable to a lens. 

 Helminthologists are not agreed as to the 

 presence of a digestive, circulating, and 

 water-vessel system in the Cestoidea and 

 Acanthocephala ; for certain tubes found in 

 them are regarded as belonging to each of 

 these systems by different authors. In most 

 of the remaining Entozoa, the digestive 

 apparatus is well developed, the mouth 

 distinct, the posterior portion of the alimen- 

 tary tube much ramified, and terminating 

 either in a csecal extremity or in a distinct 

 anus. Remarks upon these systems will be 

 found under the genera. 



Propagation. — The Entozoa are propa- 

 gated by spontaneous division, by gemma- 

 tion or the formation of gemmae, and by 

 sexual organs, and they illustrate the law of 

 alternation of generation. 



The spontaneous division, which is always 

 transverse, differs from that of the Infusoria 

 and Polypi, in the new individuals produced 

 not being perfect; a certain number of organs 

 only being reproduced, as the joints of the 

 body in the Cestoidea. 



The formation of gemmae occurs inthelarval 

 forms of TcBnia, Canurus and Echinococcns. 



In those Entozoa which are propagated 

 by sexes, the individuals are either herma- 

 phrodite or unisexual. In the Cestoidea the 

 sexual organs are usually repeated in each 

 joint, except those near the head. And it 

 appears that there are two kinds of ovaries, 

 one for the production of the germ (the 

 germinal vesicle and spot), and the other for 

 the yolk. In addition to which, there is 

 mostly a uterus, vagina, testis, penis (or 

 spiculum), and vesicula seminalis. The ova 

 are round or oval, often furnished with a 

 shell, which sometimes has a lid. 



The development of the ova of the Entozoa 

 takes place according to two methods; either 

 the yolk-mass undergoes the ordinary process 

 of segmentation, ultimately forming the em- 

 bryo ; or, large transparent embryonal cells 

 form in the j'olk, the latter not becoming 

 segmented, but undergoing subdivision and 

 diminution in size, the growth of the em- 

 bryonal cells continuing at the expense of 

 the yolk-mass until it is entirely consumed ; 

 the entire mass then becomes covered with 

 a delicate epithelium, which is sometimes 

 ciliated, and forms the embryo. 



