136 ILLINOIS BIOLOGICAL MONOGRAPHS [424 



and middle portions of the strobila and not posteriorly where the segments 

 are very short and crowded close together longitudinally, even tho the latter 

 may not show the rudiments of the reproductive organs. Figure 62 is an 

 outline of a primary segment, the fifth from the scolex in this case, to show 

 this method of subdivision. Dominance of the anterior over the posterior 

 half of the segment as regards rate of division is well shown; and this is seen 

 to be applicable also to the subsegments even to those of the fourth order. 

 ''In one specimen exaniined," to continue to quote from Linton, "the first 

 six segments did not show this alternation in size. In the next fourteen seg- 

 ments, however, the alternation was quite evident. " This indicates that he 

 noted the division of the segments into subsegments but did not ascertain the 

 exact manner in which it is carried out. "The small anterior segments are 

 terete, subtriangular in outline, narrow in front, wide behind, the length 

 nearly equal to the greatest breadth. " It is rather difficult to say to what 

 segments or subsegments the latter part of this statement refers, since it 

 describes not only what is here considered to be the first primary segment, 

 i.e., the largest segment immediately behind the scolex as shown in the figure 

 26, but also many of the major subsegments of the following primary segments 

 — not all, however, since as indicated in figure 62, the dominance in division 

 mentioned above renders subsegments of the same developmental value different 

 in size. Furthermore, as regards these anterior segments it must be empha- 

 sized that their prominent or salient posterior borders are distinctly emarginate, 

 which condition, very obvious in the segments immediately behind the scolex, 

 can be followed back to the region where the segments get very broad and 

 short. Concerning this notching of the posterior border, Linton (1889:458) 

 said: "The segments of the first series are sometimes notched or crenulated 

 on the posterolateral margin, with a single median indentation; in others the 

 edge is but slightly wavy; in others it is nearly entire. " In the material at hand, 

 however, this emargination was found as just described in all of the specimens, 

 altho in much contracted strobilae it is at first sight apparently absent. ' ' The 

 succeedihg segments are much broader than long. At the widest part the 

 ratio of the breadth to the length is as much as fourteen to one. As the seg- 

 ments increase in width they become much crowded together and thickened. 

 . . . The crowding together of the median segments is not due to contraction, 

 but seems to be a permanent characteristic of the species. " Concerning the 

 posterior segments Linton noted further (1890:729) that in the dead specimen 

 taken from Histiophorus gladius, actually No. 16.461 referred to above, "The 

 margins of the strobila are apparently entire. The segments are very short, 

 with their posterior edges slightly wavy on the median segments, thus 

 suggesting those of D. plicatum. The posterior edges of the median seg- 

 ments are crowded together like the edges of the leaves of a book about 0.2mm. 

 apart. Near the posterior end they are not so closely crowded, being about 

 0.4mm. apart." (Fig. 73). Confirmatory frontal sections showed that this 

 "entire" nature of the edge of the strobila is in reality due to partial decompo- 

 sition; yet at the same time the surficial portions of the posterior borders of 



