1-80 



ENTOZOA. 



Fig. 78. they gradually become 



expanded and blended 

 with the muscular tissue. 

 In the Strongylus 

 gigaSj a slender nervous 

 ring (a, a, jig. 79) sur- 

 rounds the beginning of 

 the gullet, and a single 

 chord is continued from 

 its inferior part and ex- 

 tends in a straight line 

 along the middle of the 

 ventral aspect (c, <f) to the 

 opposite extremity of the 

 body, where a slight 

 swelling is formed im- 

 mediately anterior to the 

 anus, which is surround- 

 ed by a loop (e) analo- 

 gous to that with which 

 the nervous chord com- 

 menced. The abdominal 

 nerve is situated internal 

 to the longitudinal mus- 

 cular fibres, and is easily 

 distinguishablefromthem 

 with the naked eye by 

 its whiter colour, and the 

 slender branches (b, b) 

 which it sends off on each 

 side. These transverse 

 twigs are given off at 

 pretty regular intervals of 

 about half a line, and 

 may be traced round to 

 nearly the opposite side 

 of the body. The entire 

 nervous chord in the fe- 

 male of this species passes 

 to the left side of the 

 vulva, and does not di- 

 vide to give passage to 

 the termination of the 

 vagina, as Cloquet de- 

 scribes the corresponding 

 ventral chord to do in 

 the Ascaris Lumbricoides. 

 In the latter species, arid 

 most other Nematoidea, a dorsal nervous chord 

 is continued from the oesophageal ring down the 

 middle line of that aspect of the body corres- 

 ponding to the ventral chord on the opposite 

 aspect; but we have not found the dorsal chord 

 in the Strongylus gigas. The nervous system 

 in the latter Entozoon obviously therefore ap- 

 proximates to that of the Anellides ; but it differs 

 in the absence of the ganglions, which in all 

 the red-blooded worms unite at regular inter- 

 vals two lateral nervous columns ; it resembles 

 on the other hand most closely the simple and 

 single ventral chord in the Sipuncidus. 



Living Ascarides are sensible to different 

 mechanical stimuli applied to the surface of 

 the body, and the sudden and convulsive 

 movements which take place when alcohol, 

 Vinegar, or alum-solution are applied to the 

 mouth, would seem to imply that they possess 

 a sense of taste : to light, noise, or odour they 



Nervous system and fe- 

 male organs of genera- 

 tion of Linyuatula tae- 

 nioides, magnified. 



Commencement and termina- 

 tion of the nervous system, 

 Strongylus gigas, magnified. 



Fig. 79. are, as might be ex- 



pected from the 

 sphere of their ex- 

 istence, totally in- 

 sensible. 



In those Entozoa 

 which infest the parts 

 of an animal body, 

 where they may be 

 exposed to the influ- 

 ence of light, as the 

 gills of fishes, we 

 should not be un- 

 prepared to meet 

 with coloured eye- 

 specks, or such sim- 

 ple forms of the or- 

 gan of vision as oc- 

 cur in Infusoria and 

 other invertebrate 

 animals of a low 

 grade of organiza- 

 tion. Nordmann de- 

 tected four small 

 round ocelli, of a 

 dark-brown colour, 

 in the Gyrodactylusauriculatu!>,a.Cestoid worm, 

 found in the branchial mucus of the Bream 

 and Carp ; the eye-specks are situated a little 

 way behind the head, and "yield on pressure a 

 blackish pigment. V. Baer observed two 

 small blackish ocelli behind the orifice of the 

 mouth in the Polystomum Integerrimum, a 

 Trematode species, which infests the urinary 

 or allantoid bladder of the Frog and Toad. 

 Now this large receptacle is well known to 

 contain almost pure water ; and as the Poly- 

 stomum is very closely allied to the Planarite, 

 which habitually live in fresh water, it is pro- 

 bable that the allantoid bladder may be only 

 its occasional and accidental habitation. With 

 respect to the Planaria these are almost univer- 

 sally provided with eye-specks, varying in num- 

 ber from two, as in the P lunar ia lactea, (Jig. 

 80, A) to forty, of a brown or black colour, the 

 external covering of which is tran- 

 Fig. 80. sparent and corneous. From the 

 A experiments of M. Duges* on 

 these non-parasitic Sterelmintha, 

 we learn that when the solar light 

 is directed to the head, they escape 

 from its influence by a sudden move- 

 ment, and they also give unequi- 

 vocal, though less energetic, proofs 

 of their subjection to the influence 

 of diffused and artificial light. The 

 temporary ocelli observed in the 

 Planaria young of certain species of Dis- 

 lactea. toma^ will be presently noticed. 



* Annales des Sciences Naturelles, 1828, p. 10. 



t Conf. also Rudolph!, Synops. Entoz. p. 442, 

 where, in the description of the Scolex polymor- 

 phus, a Cestoid worm infesting the intestines of 

 Fish and Cephalopoda, he observes, " puncta duo 

 volo corporis albi sanguinea, saepe iulgentia, qualia 

 nullis in Entozois aliis videre licuit, qua3que in 

 Gobii minuti Scolece vasa duo rubra parallela pone 

 caput incipientia et retrorsum ducta, in corpore 

 autem evanida, cffingere observavi." 



