AET. 9 MONIEZIA, A GENUS OF CESTODE WORMS TAYLOR 6 



nature of this structure ; and the same remark applies to the relative 

 position and direction of the suckers. 



2. Variations in color are only slight, and appear to depend en- 

 tirely upon the age of the worm and whether the segments have 

 reached the large intestines ; older worms are yellower and segments 

 in the large intestine become stained by the ingesta. 



The variation in the translucency of the strobila is not very great 

 and seems to be of no value. Characters which depend upon such 

 comparative terms as "a little more" or "a little less than some other 

 species" are obviously of slight value for definition, and in several 

 species the shape of head and suckers, and the color and translucency 

 of the strobila are so described. 



Characters which are a matter of numbers, and of linear measure- 

 ment can be dealt with in a more convincing manner, and there are 

 given below the two extremes of size or number of various struc- 

 tures by a series of all the intermediate measurements. If any of 

 the characters are valuable, and if there are two or more species 

 present, some evidence of their presence should be seen in a marked 

 discontinuity in the chain or intermediate variations. 



3. The nu7nher of segrnents in the stroh'da. The number of seg- 

 ments were counted in seventeen strobila of the M. expansa group 

 and the two extreme variations found to be 1136 and 2118 segments 

 for each strobila: the intermediate worms joined these two in the 

 following way, the figures representing the number of segments 

 present in each worm : 1136, 1158, 1233, 1385, 1392, 1443, 1463, 1490, 

 1511, 1565, 1579, 1581, 1886, 1918, 1944, 1969, and 2118. It will be 

 noticed that the only considerable gap is between 1581 and 1886, the 

 remainder of the series running evenly. 



4. Measurements in width of the largest segment taken from nine- 

 teen specimens of the M. expansa group were found to vary between 

 2 mm. and 8 mm., the list of measurements arranged in order being 

 as follows, the numbers representing millimeters : 2, 2.8, 3, 4, 4.5, 4.8, 

 5, 5, 5, 5.5, 6, 6, 6, 6.5, 7, 7, 7, 7.5, 8. In this series there is no marked 

 discontinuity, but a regular increase in size, the majority of the 

 worms being of a medium size. 



5. Measurements in width of head taken from seventeen specimens 

 of the M. expansa group showed a variation between 0.42 mm. and 

 0.75 mm., the whole series, given in millimeters, being as follows: 

 0.42, 0.45, 0.48, 0.495, 0.495, 0.495, 0.515, 0.525, 0.57, 0.57, 0.585, 0.60, 

 0.615, 0.63, 0.645, 0.675, 0.75. The variation in this series shows no 

 marked discontinuity. 



6. Measurements taken from seventeen specimens of the M. expansa 

 group showed a variation in length of neck between 0.15 mm. and 

 1.875 mm., the series of measurements in millimeters being as follows: 



