8 



S. ISHII : ON A NEW POLYC\"STIO GREGARI NE, 



form ; it is always somewhat shorter than the posterior tail-like part. The 

 latter is cylindrical and tapers very slightly towards the posterior end 

 which is swollen into a small terminal knob. In the young, the distinction 

 of the two deutomerite parts is not so marked as in 

 the adult, the tail being broader and the terminal 

 swelling much less conspicuous. These features of 

 the deutomerite, together with the relatively large 

 size ot the protomerite, give to 

 immature individuals an appearance 

 more or less different from that of 

 the adult. 



Between protomerite and 

 deutomerite there always exists a 

 distinct constriction, which is 

 especially marked in the younger 

 stages. Septal region pretty well 

 developed, especially so in adults. 



The epicyte of protomerite and 

 of the broad anterior part of deuto- 

 merite shows the ordinary fine 

 longitudinal striation, while in the 

 tail the same striation takes a spiral 

 course as shown in figure A. The 

 striae are much less densely 



A. Adult sporont. 

 X 260 



B. Young sporont. 

 X560 



arranged in the tail than in more anterior parts ; so that, while in the 

 latter parts at least 4 striae can be counted within a transverse extent of 

 3.7 u, in the former there may exist only two of them in the same extent of 

 space. The spiral striation takes same direction in all individuals. In 

 lateral view of these it is seen to run from the left above obliquely down- 

 wards to the right below. In the hind parts of tail the spiral winding 

 grows gradually more and more oblique, until on the terminal swelling the 

 striation is nearly meridional. In the young, the striae, besides being more 



