4G4 CYSTIC STAGE OF T^ENIA SAGINATA. 



since the occurrence of these structures in the adult tape -worms was 

 at that time all but unknown, for it was the prevailing opinion that 

 the complete absence of these structures was one of the most important 

 characters of Tcenia saginata. We have since learned that this is not 

 the case, and the above observation has thus lost much of its former im- 

 portance. But it is still of sufficient interest to claim our attention here. 



The structure just mentioned consisted of a pit-like depression, or 

 of a diverticulum from the head-cavity. It lay between the suckers, 

 and therefore belonged to the apical surface. It reminded one much 

 of the cavity of a sucker, especially since it was similarly ensheathed 

 by a muscular layer, and was of almost the same size (0*25 mm.). 

 There could be no doubt as to its nature; it was a rostellum, a 

 structure therefore which afterwards remains abortive when compared 

 with the suckers, and is thus not to be found without difficulty in 

 the adult. 



The anterior border of the apical pouch did not pass directly into 

 the cavity of the head, but was separated from it by an annular 

 diaphragm a structure which occurs at first in exactly the same way 

 in the hook-bearing bladder-worms (p. 351), but passes in the latter 

 forms ultimately into the apical lid (" Scheiteldecke "), into which the 

 basal roots of the hooks are fixed. The resemblance was all the 

 more striking since the border of the diaphragm was furnished with a 

 close circle of small points (O0035 mm.), just like those at first found 

 in the situation of the subsequent hooks in the armed forms. Here 

 and there these points were also present, deep down in the apical 

 cavity or in the suckers. 



If the structure of this organ were not the same in all bladder- 

 worms (even in those with perfectly formed suckers), one might 

 suppose that a subsequent development into the ordinary structure of 

 the hook-bearing forms took place. The facts of the case, however, only 

 admit this hypothesis on the presumption that the chronological order of 

 the developmental processes in Tcenia saginata is different from that 

 observed in the other cystic tape-worms, in which, by the time the 

 suckers are fully developed, the metamorphosis of the hooks and 

 apical plate is also almost complete. But such a presumption was 

 not in any way justified by the condition of the adult Tcenia. 



The calf experimented upon furnished material for definitely 

 investigating the development of this structure. This examination 

 was necessarily deferred for a time, so that the result might be indis- 

 putable. I therefore postponed the investigation for seven weeks, 

 until the bladder- worm might be reasonably supposed to have attained 

 maturity. One bladder-worm, which I cut out during this period 

 because it was visible through the skin of the under surface of the 



