185 
average length 0,175 mm. Three circles of six hooks each. Terminal 
hooks strongly recurved, 0,095—0,103 mm. long, points reaching beyond 
bases of middle row. Middle row 0,049—0,059 mm. long, basal ro 
0,035 —0,054 mm., average 0,043 mm. Embryos very small, Kl 
0,016 X 0,011 mm. 
In size this species presents a more striking period of growth 
from the time the final host is reached until the individuals become 
fully mature than has been observed in any other species of the genus. 
Small individuals, 2 mm. and under in length, have been found with all 
the characters of the mature form except the body size and maturity of 
the sexual products. The color is commonly milky white although 
occasionally straw and orange tinted ones are found. The hooks of the 
Figure 3. N. emydis (Leidy). Proboscis (X 145), hooks (X 465), embryos (X 465). 
Camera lucida drawing. 
second and basal rows differ from those of N. cylindratus and N. tenellus 
most sharply. In N. emydis these hooks are very much more slender 
and those of the basal row are but a trifle shorter than those of the 
second row, while for the other two species just mentioned (figs. 4 
and 5) there is considerable difference in the length of the second and 
basal rows. 
The cuticula is very thin. The subcuticula, which varies consider- 
ably in thickness, is usually about 0,140 mm. thick. In length the lem- 
nisci are invariably over twice that of the proboscis receptacle. In fully 
mature females the extent of these organs is difficult to determine on 
account of the compact masses of eggs and embryos but the study of 
sections shows them to bear the same relation to the length of the pro- 
boscis receptacle as has been found in the males and immature females. 
The receptacle of the proboscis which has its posterior end obliquely 
truncated with the apex pointed dorsad, has a length of 0,5 mm. 
The testes are very much elongated. Measurements of mature 
