HOMOLOGIES. 143 



filamentous processes, which are termed by Schmarda " stabchenformigen Korpern." The most 

 prominent features of the complex muscular arrangement filling up the body-cavity after the full 

 bulk is attained are the following : — Within the intermediate layer all round the body are many 

 longitudinal muscular bundles clasped in isolated fasciculi by divergent or curved fibres. Thus, 

 with the exception of the central digestive cavity, the whole mass of the body is filled up by 

 these interlacing, longitudinal, and other fibres. 



For some distance at the tip of the snout the stroma quite fills the region, but shortly a 

 differentiation ensues, caused by the prominence of three transverse bands of muscular fibres, 

 which pass across the snout at a distance from each other, so as to leave spaces occupied by fibres 

 which have more or less a vertical direction. At first the arrangement is merely indicated, but it 

 steadily gains so distinct a character that at last a series of spaces is left in transverse section 

 in the dorsal division. In their fully developed condition these spaces have a thick layer of 

 cellulo-granular matter, forming an inner lining or investment, which is so consistent that, in some 

 fine sections which have been torn, it remains as a ring, with a well-marked outer margin. There 

 is much opaque granular matter, also, between the vertical fibres. The channels — now larger and 

 better defined — become continuous with the anterior part of the digestive chamber. They are 

 about twenty in number in the snout. 



The long pale area (in transverse section), which forms with the preceding in the snout, 

 though streaked by the vertical granular bands, presents a much more translucent appearance. 

 Towards the tip it is a simple transverse pale belt, wider in the middle, tapering at the ends, and 

 passing entirely across the snout, the usually opaque cutaneous margin being more translucent 

 opposite the ends in such a view. At first it is more conspicuous than the dorsal belt, but after 

 the three vertical bands previously described appear, the two areas are nearly equal in breadth. 

 No aperture, however, occurs in that now under consideration. It becomes gradually more 

 transparent and wider in the middle ; and by-and-by there is a tendency to enlargement on each 

 side of the median line, while the vertical fibres forming the latter increase in prominence. A 

 pale ventral region also makes its appearance, at first faintly marked, then more distinctly; 

 the cutaneous textures, moreover, being included in the pallor. This causes the trans- 

 lucent region on each side of the median line to assume a long club -shape, and then — as an 

 increase of the opaque fibro-granular matter occurs in the centre — a wedge-shape. The central 

 septum afterwards (proceeding backwards) gets wider, a ventral prominence becomes distinct, 

 and the wedge of pale tissue shortens and assumes a somewhat ovoid form. Some pale fibres 

 stretch across the septum between each ovoid space. With a few changes as to size and separa- 

 tion this arrangement continues to the posterior end of the worm, where it gradually ceases. So 

 far as I can make out, the pale bands (just described in transverse section) are not composed of 

 nervous tissue, for which they appear to have been mistaken by Schmarda. 



The proboscis of the animal is Planarian in structure, having a glandular investment, with 

 subjacent circular and longitudinal muscular fibres — the former being most conspicuous immediately 

 below the mucous surface, and an intermediate and apparently erectile tissue. The digestive 

 tract throughout is also Planarian. It is branched in front and laterally, and towards the 

 posterior end becomes divided by a perpendicular septum into a right and a left division. 



The structure of the generative system as described by M. Claparede 1 shows a wide 

 divergence from the Nemerteans. 



1 'Mem. de la Soc. de Phys. et d'Hist. Nat. de Geneve/ tome xvi, 2eme partie, pp. 293— 312, 1862. 



