STUDIES ON THE ECTOPARASITIC TEEMATODES OF JAPAN. X9 



tliaii the other. In il/, sciac.nac the suckers of the two sides do not 

 present any considerable difference in size'^ ; but in J/, reticulata 

 those of the left side are much larger and fewer in number than tliose 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 ofave for the left side 0.227 mm. and for the riMit 0.145 mm. 



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

 riii'ht side is lonu'er and bears more suckers"'^ than the left : but 

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

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



In ])/. caudata, il/. scJ)asti^, il/, clegans, and il/, faniformis tlie 

 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 bod}^ 



In Axine the asymmetry which we have observed in the two 

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

 one of the sides of the caudal disc makes an an^le with the corres- 

 ponding side of the body proper (VI. A II), and appears like tlie 

 posterior border (the '• appendice ptéroïde " of v. Beneden). The 

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

 in A. triauijidaris (PI. All, fig. 7), tlie suckers of the two sides are 

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

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

 one (.)f the lar!xest suckers on the lon^'er side was O.GO mm. in breadth, 



1). For minuter details see description of species. 



2). Parona and Perugia (Res ligusticae, XIV, p. 38) believe that a siunlar asymmetry 

 occurs in M. enjthriiii ; but in my opinion, the supposed asymmetry in this case is 

 only apparent, having heen 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. 



