100 



LECTURE VI. 



coides, correctly states that the exterior layers of muscular fibres are 

 transverse, and tlie internal longitudinal ; the latter are arranged in 

 most Ascarides in four groups. In this large specimen of the Stron- 

 gylus gigas, which I have dissected for the muscular system, you will 

 perceive that a very thin layer of transverse fibres adlieres strongly 

 to the integument, the fibres being embedded in delicate furrows on 

 the internal surface of the skin. Within this layer, and adhering to it, 

 but less firmly than the transverse fibres do to the integument, there 

 is a thick layer of longitudinal fasciculi, which are a little separated 

 from one another, and distributed, not in eight distinct series, but 

 pretty equally over the whole internal circumference of the body. 

 Each fasciculus is seen, under a high magnifying power, to be com- 

 posed of many very fine fibres ; but these do not present the trans- 

 verse striae which are visible by the same power in the voluntary 

 muscular fibres of the higher animals. They anastomose in many 

 parts. The inner surface of the stratum of longitudinal fibres is 

 covered with a soft tissue composed of small obtuse processes, filled 

 with a pulpy substance, and containing innumerable pellucid globules. 



In the muscles of the oral booklets of the Linguatula tcenioides, 

 the fibres show the transverse striae. 



Coincident with this higher development of the muscular system 

 in the coelelminthic Entozoa is the more obvious elimination of the 

 nervous filaments, which, in the Linguatula, radiate from a distinct 

 suboesophageal ganglion. Amongst the Nematoidea the great Stron- 

 gylus is a favourable subject for the demonstration of the nervous 

 system : a slender nervous ring surrounds the beginning of the 

 gullet * ; and a single chord is continued from its inferior part, and 

 extends in a straight line along the middle of the ventral aspect to 

 the opposite extremity of the body, where a slight swelling is formed 

 immediately anterior to the anus, which is surrounded by a loop 

 analogous to that with which the nervous chord commenced, f The 

 abdominal nerve is situated internal to the longitudinal muscular 

 fibres, and is easily distinguishable from them with the naked eye by 

 its whiter colour, and the slender branches 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 female of the 

 Strongylus gigas passes to the left side of the vulva, and does not 

 divide to give passage to the termination of the vagina, as Cloquet 

 describes the corresponding ventral chord to do in the Ascaris him' 

 bricoides. In the latter species, a dorsal nervous chord has been 

 described as being continued from the oesophageal ring, down the 



* LX. p. 130. fig. 79. a. f lb. e. 



