No. 5.] THE CESTODE MOXIEZIA EXPANSA. 233 



separated to a certain degree on this side, are still much less 

 distinct than normal segments, and the pores and terminal por- 

 tions of the ducts of a' are therefore found in a position only a 

 little posterior to that which they would occupy if a and b were 

 not separated at all. 



The partial segment b, as marked off by the slight and inter- 

 rupted dorsal furrow, is narrower than a. The complete set of 

 organs, a', lies nearly in the middle of a b, but since the two 

 segments are sufficiently distinct dorsally for the formation of a 

 slight furrow, there is a certain tendency for another set of those 

 organs which lie near the dorsal surface to form in b, as is indi- 

 cated by the presence of a pore with atrium and cirrus at the 

 edge, and the inner portion of the vas deferens at b'. These 

 parts are wholly unconnected, and there is no trace of female 

 organs. The failure to develop a complete vas deferens is 

 probably clue to the fact that the segment b, as bounded dorsally, 

 is of less than normal length and imperfectly separated from a. 

 The parts of the male organs which do appear are identical with 

 those which we find in Fig. 10, b, but in that case there is a 

 trace of female organs also. These two cases are examples of a 

 condition often found in short, imperfectly separated segments, 

 viz., the development of the innermost and outermost portions 

 of the organs without connection. It appears as if the region of 

 the pore and the inner portions of the ducts represent, as it were, 

 the places of least resistance with respect to the formation of 

 the genital organs, so that segments which are not sufficiently 

 normal to give rise to a complete functional set of organs may 

 form these two parts, but not the ducts connecting them. 



The complete absence of female organs at the right of b shows 

 very clearly that the formation of the ovary and vitellarium is 

 connected with the conditions on the ventral side of the body, 

 and the formation of the vas deferens with conditions on the 

 dorsal side. 



The shallow dorsal interrupted furrow at the right is without 

 inter-proglottidal glands, probably because of its slight develop- 

 ment. 



