90 M. L. Plate on Ectoparasitic Rotatoria 



again. Fig. 1 represents an individual engaged in wandering, 

 and it shows at the same time that the side turned towards 

 the support must be regarded as the helly. 



The limitation of the four sections of the bodj distinguished 

 in the preceding description cannot be followed out quite 

 sharply, as they gradually pass one into the other. Tiiis 

 applies especially to the two posterior divisions ; it seems 

 therefore advisable to reckon the foot as extending as far as 

 the adhesive glands which give it its function extend forward 

 (/'). The female genital orifice then indeed falls within the 

 region of the tail, which moreover is marked by a peculiar 

 habit of the Paraseison during life. Thus, when the animal 

 is disturbed or finds itself in an uncomfortable position, e. g. 

 on the object-slide, the body almost invariably forms an angle, 

 usually re}5resenting nearly a right angle, one limb of which 

 is formed by the tail alone ; its apex, as shown in fig. 1, is 

 situated a little above the sexual aperture [a). This singular 

 position is explained anatomically by the fact that the prin- 

 cipal muscles of the trunk and abdomen meet in the region 

 of this apical point, and it is further evidently connected 

 with the absence of a rotatory apparatus, which compels the 

 animal to seek its nourishment by feeling about with its head 

 upon the support ,* it presents a peculiar spectacle to see the 

 disproportioned animalcule in a bent posture stretching its 

 long swan-like neck in all directions, and every moment 

 retracting it completely into the trunk. 



After this introductory glance at the structure of Para- 

 seison asplanchnus we may pass to a more detailed description 

 of the different organs. 1 commence with the general 

 covering of the body. 



The tSkin. — This possesses all the properties characteristic 

 of the body-wall of the freshwater Rotatoria. It consists of 

 a thin hyaline cuticle, which is coated internally with a deli- 

 cate protoplasmic matrix-layer, in which small nuclei with a 

 large nucleolus are scattered here and there. This hypo- 

 dermis is in parts so extraordinarily thin that we can only 

 detect it with very high powers. Nevertheless it could be 

 demonstrated everywhere, and probably therefore the species 

 of Seison also present the same character, although Claus 

 observes that " subcuticular traces are retained only in a few 

 places in the form of granular pads." At the extreme apex 

 of the head, close to the buccal aperture, the matrix of Para- 

 seison becomes thickened into pads, evidently the rudimentary 

 homologues of the cephalic pads bearing the rotatory appa- 

 ratus in the freshwater forms. Special cutaneous glands, such 

 as are said to occur in Seison, are quite absent in our animal, 



