136 



ENTOZOA. 



cms at the posterior part of the body. The 

 nervous Chord passes at a right angle to the 

 transverse bands between them and the longi- 

 tudinal muscles, and sometimes is included in 

 loops of the former, as at d, jig. 88. Both the 

 pendant processes and the transverse bands are 

 composed of a homogeneous spongy tissue, 

 without any central cavity, and appear to form 

 a nidus of nutrient matter like the fatty omen- 

 tal processes in higher animals. 



The longitudinal lines (c,c,fg. 86,88), which 

 extend along each side the body of the Ascaris 

 Lumbricoides, and which are very conspicuous 



Fig. 88. 



Nutritive processes and vascular canals magnified, 

 Ascaris lumbricoides. 



externally through the transparent integument, 

 consist each of a narrow flattened tract of opaque 

 substance, by some anatomists considered as 

 nervous, and a very slender vessel which ad- 

 heres closely to the outer side of the band. 

 The two bands become expanded at the an- 

 terior extremity of the body, and unite in 

 forming a circle around the oesophagus : the 

 vessels, on the contrary, become detached from 

 the bands, and pass transversely below the 

 oesophagus to anastomose together, forming a 

 simple loop or arch, the convexity of which is 

 anterior. By pressure the reddish fluid con- 

 tained in these vessels may be made to tra- 

 verse them backwards and forwards. 



With respect to the accessory glands of the 

 digestive system of the Entozoa, I have hi- 

 therto met with tliem in two species only of 

 the Neinatoidea, in both of which they pre- 

 sented the primitive form of simple elongated 



unbranched cceca. The first being developed 

 from the commencement of the alimentary 

 canal, and co-existing with a pair of rudimen- 

 tal jaws, must be regarded as salivary organs. 

 They exist in a species of worm which 

 infests the stomach of the Tiger, and which 

 I have recently described under the name 

 of Gnattiostoma aculcatum* They consist 

 of four slender elongated cceca, communi- 

 cating with the mouth, and gradually increas- 

 ing in size as they extend backwards into the 

 abdominal cavity, where they end each in a 

 cul-de-sac ; they are placed at equal distances 

 around the alimentary canal, and have no at- 

 tachment except at their open anterior extre- 

 mity. The length of each coecum is about 

 one-twentieth of the entire alimentary canal. 

 Their parietes under a high magnifying power 

 present a beautiful arrangement of spirally 

 decussating fibres. Their contents when recent 

 are clear, but become opaque when immersed 

 in alcohol. That the Gnatkostoma is not the 

 larva of an insect is proved by the complete 

 development of the generative system, which 

 resembles that of the Ascarides, and by the 

 absence of a ganglionic nervous system. 



The second example of an accessory digestive 

 gland occurs in a species of Ascaris infesting 

 the stomach of the Dugong : here a single 

 elongated ccecum is developed from the in- 

 testine at a distance of half an inch from the 

 mouth ; and is continued upwards, lying by 

 the side of the beginning of the intestine, with 

 its blind extremity close to the mouth ; from 

 the position where the secretion of this ccecum 

 enters the intestine, it may be regarded as re- 

 presenting a rudimental liver.f 



Respiratory Organs. The Entozoa have no 

 distinct internal or external organs of respi- 

 ration. The skin in many of the Trematoda 

 and Acunt/wcep/iala is highly vascular,! and 

 the circulating fluids in these worms may be- 

 come oxygenated by contact with the vascular 

 mucous membranes of the higher organized 

 animals which they infest. In the Planaria 

 the surrounding water is renewed upon the 

 vascular surface of the body by means of the 

 currents excited by the action of vibratile 

 cilia; and the young of certain species of 

 Distomata, which pass the first epoch of their 

 existence under the form of Polygastric In- 

 fusoria, freely moving in water, are pro- 

 vided with superficial vibratile cilia arranged 

 in longitudinal rows; but these organs of lo- 

 comotion and adjuncts to the respiratory pro- 

 cess are lost when the Distomata resume their 

 position as parasites in the intestines of the 

 Fishes from which they were originally ex- 

 pelled. 



Excretory glands. As an example of an 

 organ of excretion, we may refer to the glan- 

 dular sac lodged in the enlarged extremity of 

 the Distoma clavatum, which opens externally 



* Proceedings of the Zoological Society, Nov. 

 1836. 



t See the Preparation, No. 429 A, Mus. Coll. 

 Surgeons, Phys. Catalogue, p. 121. 



} Conf. Echinorhym hus vasculosus,Entoz.Synop. 

 p. 581. 



