FORMATION OF PROGLOTTID3 IN CROSSOBOTHRIUM. 219 



to be something which affected the anterior end of the strobilla 

 independently of the origin of the proglottids involved. 



It has occurred to me in collecting the worms from the spiral 

 valve that perhaps the four projections which characterized these 

 forward segments of the adult strobilla, may be regarded as an 

 adaptation by which the worm is better able to retain its hold 

 with the scolex. The passage along between the folds of the 

 semi-solid feces which are often found in the valve, must often 

 draw out the bodies of these cestodes and tax the hold of the 

 scolex to a corresponding degree. The projections in ques- 

 tion would be very effective in preventing the front part of the 

 worm from slipping backward and would thus relieve the strain 

 on the scolex. I believe that we must look to something in the 

 conditions which act upon the anterior region of the strobilla and 

 not to the anterior or posterior origin of any given proglottid, 

 to account for this feature of C. laciniatnm and the above sug- 

 gestion is given as a possible explanation. 



Since the theories regarding the nature of the cestode body 

 have taken into consideration the supposed universal method of 

 proglottid formation we may consider what bearing the facts here 

 established have upon such theories. At the outset I will say 

 that I do not think this single case of a small number of true 

 proglottids developed anteriorly and in the reverse direction will 

 justify any sweeping modification of existing views, for it is only 

 fair to suppose that the posterior proglottids of C. laciniatum are 

 strictly homologous to the entire strobilla in other cestodes and 

 we may regard C. laciniatum as a species in which another 

 method of proglottid formation has been superposed on an older 

 and more universal one. The history of our theories regarding 

 the nature of the cestode body is extensively summarized by 

 Braun in the Cestode volume of Bronn's Thierreich. Beginning 

 with the earlier conception of the chain as composed of pro- 

 glottids which had become united, he traces the history of the 

 theory developed by J. P. van Beneden, Siebold, Leuckart and 

 others, which viewed the Cestode at a " polyzootic ' organism, 

 /. t\, that despite the physiological unity of the chain of proglot- 

 tids we are dealing, from the morphological standpoint, not with 

 a unity but with an animal stock. This view has been main.- 



