STUDIES OS THE ECTOPARASITIC TREMATODES OF JAPAN. J 9 



than the other. In M. sciaenae the suckers of the two sides do not 

 present any considerable diiference in size'' ; bat in M. reticulata 

 those of the left side are much larger and fewer in number than those of 

 the other. Thus, in the latter species a measurement of the breadths of 

 the corresponding suckers of the two sides at about the middle of the 

 caudal disc gave for the left side 0.227 mm, and for the right 0.145 mm. 



In the specimens of the two species figured on the plates the 

 right side is longer and bears mpre suckers^' than the left ; but 

 whether this is' constantly the case or not I have not had a suflficient 

 number of specimens to decide (cf. infra de Axine). 



In M. caudata, M. sebastis, M. elegans, and M. fusiformis the 

 caudal disc extends for some distance anteriorly from the point 

 where it becomes continuous with the body proper ; but in all the other 

 species it does -not, and the suckers are arranged merely along the 

 lateral margins of the body. 



In Axine the asymmetry which we have observed in the two 

 species of Microcotyle above mentioned is carried one step farther, and 

 one of the sides of the caudal disc makes an angle with the corres- 

 ponding side of the body proper (PI. VII), and appears like the 

 postei'ior border (the "appendice pteroide" of v. Beneden). The 

 other side bears only a small number of suckers. In some species, as 

 in A. triangularis (PI. VII, fig. 7), the suckers of the two sides are 

 nearly of the same size ; but in A. lieterocerca. (PI. VII, fig. 1) they 

 are of very dififerent sizes on the two sides. Thus in one specimen, 

 one of the largest suckers on the longer side was 0.60 mm. in breadthj 



1). For minuter details see description of species. 



2). Parona and Perugia (Res ligustioae, XIV, p. 38) beUeve that a similar asymmetry- 

 occurs in M. erxjthrini; but in. my opiiiion, the supposed asymmetry In this case is 

 only apparent, having been caused by pressure and the twisting of the body at the point of 

 attachment of the caudal disc, as occurs very often when the worm- is observed under the 

 cover-slip. The real asymmetry could only be caused by the unequal length of the sucker- 

 bearing portion of the two sides, and there is none in the species in question. 



