F. J. Meggitt 
9 
A single set of reproductive organs in each segment. Genital pores unilateral 
or alternating 1 . Uterus persistent ( D . uterina Fuhr.), or transient: in the 
latter case the eggs are either enclosed in egg-capsules or are scattered through¬ 
out the parenchyma (D. rhynchola Rans.). Eggs with thin transparent shells. 
Adults in mammals or birds. Larval stage a cysticercoid parasitic in molluscs 
or insects. Type species— Davainea proglottina (Davaine, 1860). 
The species of the genus fall roughly into four classes, the division being 
based upon the armature of the suckers, and the position of the genital pores. 
Aa. Genital pores unilateral, suckers armed. 
Ab. Genital pores unilateral, suckers unarmed. 
Ba. Genital pores alternating, suckers armed. 
Bb. Genital pores alternating, suckers unarmed. 
This division, while useful for dealing with a large number of species and 
for identification, cannot be regarded as wholly natural. The armature of 
the suckers is very transient and many of the species at present said to possess 
unarmed suckers may, when their life-histories are fully known, be found to 
lose their acetabular hooks at an early stage. Neither is the position of the 
genital pores a character altogether suitable for the characterisation of sub¬ 
genera. D. tetragona (Mol.) possesses unilateral genital pores and D. echinobo- 
tlnrida (Meg.) alternating pores in the adult form and unilateral in the young. 
The two species are closely related and no classification can be regarded as 
satisfactory which separates them. A character upon which a classification 
may perhaps be finally based is the behaviour of the uterus and the origin 
of the egg-capsules. A large number of species have egg-capsules each con¬ 
taining only one egg (e.g. D. cesticillus Mol., D. corvina Fuhr., D. microcotyle 
Skrj.), others possess from two (D. celebensis Jan., D. friedbergi Lins.) 
to 14 or 15 eggs per capsule (D. oligorchidna Fuhr., D. salmoni Stiles): in 
D. insignis Steudener (1877, p. 302)—“Der Uterus dehnt sich dann mehr 
und mehr aus und bildet schliesslich einen die ganze Mittelschichte des Gliedes 
einnehmenden Sack, in welchen die Eier durch eine kornige Substanz zu 
Conglomeraten verbunden sind,” and in D. uniuterina (Fuhrmann, 1909, 
p. 114)—“Der Uterus scheint sich nicht (oder sehr spat) in einselne Paren- 
chymkapseln aufzulosen, sondern als einheitlicher, stark gelappter Uterus 
bestehen zu bleiben,” while in D. rhynchota Ransom (1909, p. 14), distinctly 
states that the eggs are scattered singly throughout the parenchyma and are 
not enclosed in capsules. Beddard (1914, pp. 875 and 885) again considers 
the egg-capsules as formed by a number of parauterine organs. Unfortunately 
our knowledge of the behaviour of the uterus in this genus is not sufficiently 
extensive to allow of the utilisation of this character. Its structure and be¬ 
haviour in many of the species are entirely unknown and in others but 
insufficiently described. All our knowledge of D. difformis (Rud.) is contained 
in a statement by Fuhrmann (1908, p. 45), “Rudolphi nannte diese Art 
1 Ransom ( loc. cit) states the genital pores occasionally alternate. 
