Our Fresh-Water Planarice. 447 



Planarian worms, for they can contract and "elongate their 

 bodies, fold themselves together in various forms, and unfold 

 themselves, we naturally expect to find the presence of mus- 

 cular fibres ; how can such movements be explained except 

 by the admission of the existence of a muscular system ? And 

 yet there are some animals of low organization, such as the 

 small species of the Trematocla, which are endowed with 

 active contractility, in whose bodies, notwithstanding, no mus- 

 cular fibres have been detected. With respect to the Planarice 

 many observers, as de Blainville, Duges and others, entirely 

 deny the existence of a muscular system, except in the pro- 

 boscis, and genital organs ; M. Quatrefages, on the other hand, 

 describes a sub-cutaneous plane of muscular fibre, as being 

 recognisable in some species, and Professor Owen remarks that 

 in the Planarice, in which as in the Teenies, according to his 

 observations, the muscular system is indicated only by the 

 strias on the superfices of the apparently homogeneous 

 parenchyma, the phenomena of muscularity are strikingly 

 displayed in the varied and energetic actions of the living 

 animal.* My own investigations have satisfied me of the 

 existence of a sub-cutaneous plane of loose muscular fibre in 

 the fresh-water genera, Planaria and Polycelis. A nervous 

 system in some species has been recognised by de Quatrefages, 

 who describes it as " consisting of two ganglions, more or less 

 intimately united, which are situated in the mesial line, near 

 the anterior part of the body. This double ganglion, which 

 may be called the brain, and which is sometimes visible to the 

 naked eye, is lodged in a special lacuna or cavity, recognisable 

 from its transparent outline, and is seen to give off nervous 

 filaments in various directions to different parts of the body/'f 

 In vain have I laboured in search of the faintest indications of 

 a nervous system in the species I have examined. The 

 relation of the Planarice to the Flukes, as already noticed, 

 might lead us to expect the existence of a rudimentary nervous 

 system in them as in those Entozoa, nevertheless, I think that 

 we must still consider its presence in the fresh-water species 

 as a subject requiring verification. Professor Rolleston, who, 

 at my request, kindly repeated his examination of many speci- 

 mens of Planaria lactea, says, " With reference to the nervous 

 system of this species, I have never been quite satisfied that it 

 was a real existent thing. Leydig says he has failed to see it 

 sometimes in the fresh-water Planarice ; but that the analogy of 

 the marine Planarice, where a nerve- system is undoubtedly 

 present, has forced him to look for it, aud that he believes that 

 a couple of pear-shaped ganglia underlying the two eyes, and 



* Todd's "Cyl. of Anat." n„ p. 128. 



f Rymer Jones, " General Structure," p. 146. 



