152 CHILD. 



Cestodes. This condition is perhaps connected in some manner 

 with the fundamental structural or physiological characteristics of 

 the form. 



An inquiry as to the causes of the frequency of form-variations 

 in Moniezia may therefore concern itself first with the normal 

 anatomy and physiology. A few suggestions as to some of the 

 possible factors concerned are made here in the hope of throwing 

 some light upon this problem. First, the method of formation of 

 the proglottid, its appearance in two separate parts which later 

 unite, must favor to some extent the development of abnormalities, 

 for a slight variation in position or time of appearance of the anlagen 

 may apparently effect the extension and union of the anlagen of 

 the two sides. It is not known at present whether the proglott- 

 ids of all other Cestodes arise in the same manner. If in some 

 the proglottids originate in a single group of cells the chances for 

 abnormal development would apparently be fewer. Second, the 

 form of the proglottids, the great width in proportion to the 

 length favors the appearance of abnormalities. In the early 

 stages the proglottids are extremely short and it is evident 

 that abnormal union of right and left anlagen must occur more 

 frequently than in forms with longer proglottids. Third, it is 

 possible that the proglottids of Moniezia possess a lower degree 

 of individuality than those of some other Cestodes, /. t\, that they 

 are less distinct structurally and physiologically. If this is the 

 case then incomplete separation may be expected to occur more 

 commonly than in forms with more highly individualized pro- 

 glottids. 



The frequency of form-variations differs greatly in different 

 specimens. More than half of the cases shown in Parts I. and 

 II. were taken from a single chain and represent only a part of 

 the abnormalities present. Other specimens possess in most 

 cases only a few abnormal proglottids, but nearly every specimen 

 exhibits one or two. We have at present no clue to the cause 

 of this difference. It is possible that age may have some influ- 

 ence, the older specimens showing a tendency to incomplete 

 development. Injuries to the neck-region, or the repeated tear- 

 ing away of the whole body, or perhaps malnutrition, may also 

 favor the appearance of abnormalities, and finally these differences 



