253 
containing the reproductive organs. With few exceptions this sac pre- 
sents the same external appearance in different species, though members 
of some genera are readily distinguishable by the presence of spines upon 
the body-covering. General body-shape and size differ with the age of the 
individuals, but certain features of body-form are of value in the recog- 
nition of species if used in connection with other characters of a more 
stable nature. In view of this fact, outline drawings of entire individuals 
of many of the species are presented, for the first time, in this paper. 
Unfortunately, the proboscis, upon which much importance is placed 
in classification, is frequently completely invaginated within the body. 
Living specimens may be induced to protrude the proboscis if left for a 
few minutes in a dish of plain water, though they are best studied in 
normal salt-solution. 
Stained whole-mounts and sections are needed for the study of 
internal organs and for an accurate study of the proboscis hooks. Pre- 
liminary to the preparation of these, the worms should be placed for 
about fifteen minutes in a saturated solution of corrosive sublimate to 
which enough acetic acid has been added to make a one per cent. mixture. 
After washing in water the specimens should be passed through 35 and 
50, to 70 per cent. alcohol in which they may be kept indefinitely. In the 
preparation of whole mounts and of sections ordinary histological pro- 
cedure is followed. Best results are obtained if the body wall is pierced 
in a number of places with a fine needle. This prevents shrinkage when 
specimens are changed from one liquid to another. A very dilute mixture 
of Ehrlich’s acid hematoxylin in distilled water has been found to be one 
of the most valuable stains for whole mounts in damar and for sections. 
In the following key an attempt has been made to utilize characters 
which are easily observable even in living or in alcoholic specimens. In 
most instances, however, the separation of species involves careful study 
of permanent mounts and of sections. 
Key To SPECIES FROM FRESH-WATER VERTEBRATES EXCLUSIVE OF Birps 
1(24) Body proper devoid of spines—an elongated sac, approximately circular 
in cross-section; surface smooth or slightly folded to produce slight 
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2 (3) Anteriorly the body proper passes over into a long cylindrical neck of 
considerably smaller diameter than the body. In freed specimens the 
anterior extremity of neck shows a spherical enlargement. Proboscis 
and this enlargement both usually embedded in the tissue of host 
intestine. Host a fish...... Pomphorhynchus bulbocolli Linkins, n. sp. 
3 (2) Diameter of neck not conspicuously smaller than that of body proper. 
Neck never bearing a spherical enlargement..............-....00.. 4 
4(15) Proboscis globular, bearing three circles of hooks. Body frequently 
showing slight protuberances along mid-dorsal line, indicating posi- 
tions of giant nuclei. Cement gland of male a single syncytial mass. .5 
5 (6) Parasitic in intestine of turtles............Neoechinorhynchus emydis. 
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