Anatomical structure of Aspidogaster conchicola. 4Ô3 



number of oblong, square, or otherwise shaped little fields concave 

 ventralwards (alveoli, Macdonald ; acetabula, Leidy; quadrate fossettes, 

 Dujardin). Each one of these alveoli is physiologically a sucker but 

 morphologically only a part of a specialized posterior or ventral 

 sucker. The number of fossettes varies with the number of transverse 

 ridges which latter increase with the age of the animal. The embryo 

 possesses only a single, simple posterior sucker. The greatest number 

 of acetabula that I have counted in the adult is 118 i. e. when there 

 would be 31 cross walls. 



The sucker as a whole is sharply separated from the parenchyma 

 of the body above by a limiting membrane (Fig. 4, 5, 6 LM) in which I 

 have recognized delicate, upper horizontal and lower longitudinal fibres. 

 This membrane dips down between the alveoli a short distance, 

 repeating the general course of the cuticular surface below the sucker. 

 In it are interknit the inferior ends of the infra-septal parenchyma- 

 muscles, described above, and the upper ends of certain muscles of the 

 sucker, later to be mentioned. The walls of the alveoli have a like 

 structure except for unimportant differences which are occasioned by 

 the marginal or end positions of the outer row. A single alveolus 

 measures under ordinary conditions of contraction of the fixed animal 

 about 0,15 mm broad (0,1 to 0,17) between the centres of two longitudinal 

 walls, and 0,05 mm long (0,04 to 0,07), and from cuticle to limiting mem- 

 brane is 0,05 mm. Each one exhibits in transverse section vertical 

 fibres (Fig. 2, 4, 5, 6) extending between the thin cuticle below and 

 the limiting membrane above. Frequently it can be seen that these 

 are split at the ends. The longitudinal ridges (Fig. 2, 7 LR) hang 

 down like inverted cones and extending across these are transverse 

 muscleSi Just above the cuticle and between its toothed upward pro- 

 jections — attachments of the vertical muscles — are shown trans- 

 sected longitudinal muscles. Where a section passes through the 

 whole length of one of the transverse ridges can be seen several rows 

 of sectioned longitudinal fibres. A longitudinal (sagittal) section in- 

 dicates the same series of muscles only that the longitudinal (Fig. 4, 

 5 LF) and transverse (Fig. 4, 5 TF) muscles have changed place in 

 that now one sees the former from the side and the latter in cross 

 section. Two rows of fibres, that separate contiguous alveoli, slant 

 down from the point of the depression in the limiting membrane to 

 the sides of the cross wall including between them a triangular space 

 resting with its base on the transverse ridge. In these spaces are 

 situated, on the margins of the sucking disk, at the ends of every 



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