252 
TABLE VI 
Data rroM DEscRIPTIONS oF N. rutili anv E. clavacceps 
(Measurements are in p) 
| Length of hooks 
Author Date | Species E 
eee Terminal] Middle | Basal ee 
I 
Tihewsnln ces 1911 |rutili 170 100 [100?] | 38 by 19-21 
Hamann...... 1891 |clavaeceps 70 30 [30?] 41 
Porta cries cis uss 1905 |clavaeceps 70 30 [307] 35 by 17 
Dujardin...... 1845 |clavaeceps 67 44 41 41 
The fresh-water representatives of this genus in Europe truly need 
the attention of some careful worker to ascertain if all belong to the same 
species. If Lihe’s synonymy is correct some one should study the inter- 
esting case of variability in N.rutili since he reports specimens having 
terminal hooks 170 » long, while Hamann found that typical individuals 
had hooks but 70 » long. If one could have implicit faith in the data pre- 
sented by these authors there would be ample ground for the recognition 
of two distinct species; but their descriptions are too inconsistent and 
contradictory to justify such a course. Hamann (1891, Pl. IX, Fig. 3) 
figures the terminal hooks of E.clavaeceps as less than 50 per cent. 
longer than the hooks of the middle circle, while in the same article he 
describes them as more than twice as long. Similarly, in Figure 17 of 
the same plate he shows the terminal hooks as only 25 per cent. longer 
than those of the middle circle. Ltthe (1911, Fig. 2) obviously made an 
error in the calculation of the magnification of his drawing of the pro- 
boscis of N. rutili. On the basis of the stated magnification the terminal 
hooks are only 64 » long, instead of 170 » as stated in the text. 
Since N.rutili is regarded as the type of the genus, it is an unfor- 
tunate circumstance that there is so great lack of agreement in the avail- 
able descriptions. If Porta, Dujardin, and Hamann are correct, the chief 
means of distinguishing this species from N.agilis lies in the smaller 
size of the terminal proboscis-hooks of the former, though Ltuhe would 
have us believe that the chief distinction lies in the larger terminal-hooks 
of rutili. Bieler has offered one means of separating N. agilis and N. rutili 
based upon the number of giant nuclei in the cement gland of the male, 
but he simply states that the former has eight giant nuclei while the latter 
has twelve. He has given no statement of other diagnostic features avail- 
able for the separation or characterization of the species. 
Tue IDENTIFICATION OF SPECIES 
The Acanthocephala present few characteristics available for ready 
identification of species. Through adaptation to the parasitic habit the 
body proper has become reduced to little more than an elongated sac 
