FORMATION OF PROGLOTTIDS IN CROSSOBOTHRIUM. 2 17 



the muscle fibers are less developed. In the young worm the 

 zone has a circular outline in section while in the neck region it 

 is somewhat flattened. Fig. 26 which represents the structures 

 found in this zone of a young worm shows that there occur only 

 the structures which are regarded as typical for the adult cestode 

 (Schneider, '02, p. 311, Fig. 324, and Braun, PI. XLVII.). 

 There are circular and longitudinal muscle fibers between the 

 cuticle and the palisade of subcuticular cells, the latter being 

 grouped so that they form lines between the outer portions of 

 these cells. The parenchyma contains scattered nuclei, some with 

 cytoplasm aggregated about them as in a definite cell body. 

 One member of each pair of water tubes appears in the figure. 

 The results of this examination are disappointing, for unless there 

 is an active amitotic division, which I fail to make out with this 

 material, there is nothing which would suggest the active differ- 

 entiation which is taking place. However, I do not offer this 

 as in any way an adequate discussion of the histology of this 

 region. Such an account I hope to give at some future time 

 when I have proper material for a thorough examination. This 

 is merely a statement of what I have been able to accomplish 

 along this line thus far. 



IV. GENERAL CONSIDERATIONS. 



If my interpretation of the stages found is correct, we have in 

 Crossobothrium ladniatum a method of proglottid formation which 

 is radically different from the one now accepted as universal. 

 Also, there seems to be more than one strobilla formed so that 

 we may speak of primary and secondary strobillas and perhaps 

 there are even more. This is in marked contrast with such 

 forms as the tsenias which present a continuous growth and dif- 

 ferentiation in the neck region to make good a continuous shed- 

 ding of ripe proglottids. If we try to analyze the proglottid 

 formation here described and to compare it with the process 

 which occurs in other cestodes, we may do so in the following 

 way. The appearance of the first proglottids at the posterior end 

 is homologous to the method now accepted as the universal one. 

 Such a stage as is shown by Fig. 5, PI. IV., and from this on to 

 the time when the " anterior" proglottids begin to appear, may 



