72 ANATOMY OF THE ENOPLA. 



entering into its composition as the anterior region, though, he adds, the muscular layers are pro- 

 portionally thinner. As already stated, the structure of the walls of the two regions is essentially 

 different, just as their functions disagree. He is correct in averring that the cavity ends in a 

 cul-de-sac ; but wrong in saying it is ciliated, and that the terminal ribands are attached " a la 

 paroi abdominale." Lastly, he is only certain of the muscularity of these ribands in Folia coronata 

 {Tetrastemma melanocephala), and he gives a curious figure (which cannot be verified in our 

 specimens) of their termination as a series of arborescent fibres. This author also considered that 

 the marginal sacs secreted stylets for the supply of the central apparatus. 



Dr. Johnston's description of the stylet-region is as follows : — " First, we perceive on each 

 side a small circular spot or cavity, in each of which are three spines with their sharp points 

 directed outwards; beneath these there is a cup-shaped organ encircled above with a faintly 

 plaited membrane, and armed in the centre with a strong spine, which can be compared to 

 nothing more aptly than a cobbler's awl in miniature, the part representing the handle being very 

 dark, and the point transparent and crystalline. This apparatus is placed within the intestine, 

 is visible only when this is compressed, and is, as I believe, stomachial, having some distant 

 analogy with the proper digestive organs of Laplysia and Bulla." His anatomy is thus 

 imperfect ; and he, moreover, held the opinion that the " intestine/' as he termed the organ, 

 proceeded to the tip of the body and terminated in a distinct anus. 



Dr. Thomas Williams observes with regard to the proboscis (his digestive tract) : — " The 

 extremity of this organ is armed with several styleted jaws, which, from their construction, seem 

 only designed to fix the suctorial end by perforating the alimentary object. When the proboscis 

 is withdrawn into the interior of the body, fitting admirably into a short oesophagus, these sharp 

 instruments are packed and folded upon themselves," the sides of the tubes closing round them. 

 The correct examination of a single extruded organ would have at once dispelled such notions. 

 His supposition, that the glands in the interior of this structure furnish an important secretion for 

 the digestive process, which secretion is exuded into the " oesophagus" (apparently, judging from 

 his figure, the proboscidian sheath), and thence into the great alimentary organ, rests upon no 

 facts. He also errs in stating that the outlet of this organ is situated not far from the cephalic 

 end of the body; but his remark, that there is no open communication between the oesophageal 

 tube (proboscidian sheath) and the " alimentary caecum," is correct. 



Dr. Max S. Schultze, in his account of Tetrastemma ohscwum, gives no definite description 

 of the ending of the proboscis, and figures the central stylet as projecting freely into the cavity. 

 He indicates the presence of the muscular space behind, but confounds its structure with the 

 wedge-shaped investment of the basal apparatus, the whole forming, he remarks, a quadrangular 

 mass. He erroneously describes the terminal ribands as attached to the wall of the body. In his 

 figure he omits to notice the ducts of the marginal sacs, though he regards the latter as the 

 producers of the stylets for the central organ. He first indicates, however, the connection 

 between the developing spikes and the clear globules in the marginal sacs, showing that they are 

 sometimes seen in their interior. Finally, he has not discriminated the structure of the reservoir 

 and its relations to the neighbouring parts ; and, indeed, his anatomy of the organ, from 

 the limited nature of his observations, is somewhat imperfect. These remarks apply to his 

 ' Beitrage,' as well as to his more recent representations in the ' Icones Zootomies.' 



M. Claparede describes, in his e Recherches Anatomiques/ the apparatus of the central stylet in 

 Tetrastemma varicolor as set in a pale space of a triangular form, and he leaves the stylet- 



