FORMATION OF PROGLOTTIDS IN CROSSOBOTHRIUM. 211 



of the margins. This condition is continued for a distance shown 

 by the line /", before the rudiments of the reproductive organs are 

 clearly discernible. When a place is reached where these can 

 be definitely made out (Fig. 14, g) it is seen that the proglottids 

 are beginning to assume the outlines characteristic for the pos- 

 terior members of the chain. In g of Fig. 14, we find the repro- 

 ductive organs well marked out at the region just in front of the 

 386th proglottid. They are first apparent in the whole mount 

 at about the region of the 325th proglottid. From the region 

 shown by g of Fig. 14 to the posterior end the transition along 

 /land i to the 4/ist at j is gradual and from this latter point 

 through /', / and ;//, to the terminal region, shown by n of 

 Fig. 14, the change consists more in the elongation of the pro- 

 glottid than in its growth in bulk. The 5o6th proglottid which 

 terminates the chain shows fully developed reproductive organs 

 and some eggs accumulated in the uterus and is farther advanced 



o o 



than many of the free motile proglottids one finds in the intestine. 



(c) TJie Reduction of the Primary Strobilla ami tlic Formation 

 of the " Long-necked" Stage. Such a specimen as the one just 

 described may be termed a yonng adult, for it still has about the 

 number of proglottids which we have reason to believe is not far 

 below the maximum and it is already liberating ripe segments 

 from the posterior end. The following points are of importance 

 in this connection : First, the reproductive organs do not begin 

 until well back of the 3OOth proglottid. Though sections might 

 show them being laid down in front of this region, there is in 

 any case a long region extending beyond the anterior half of the 

 worm in which they have not yet appeared. Second, the non- 

 segmented zone has been obliterated and the place where it dis- 

 appeared can no longer be recognized. Third, there is no point 

 in the chain where there is anything to suggest the interpolation 

 of new segments. I have examined a large number of speci- 

 mens in this and in the stages next succeeding without finding 

 the slightest indication that new proglottids are added in the 

 region back of the solex or elsewhere. 



The only change which takes place in such a specimen is the 

 continual dropping off of ripe proglottids from the posterior end 

 and the steady advance toward the scolex of the region of ap- 



