22 
THE VOYAGE OF H.M.S. CHALLENGER. 
cavity divided into paired chambers by incomplete septa. Usually four 
pairs of suckers. Hermaphrodite or dioecious. Ova evacuated through 
a cloaca, male generative apertures situated laterally. 
Of the first Family we have at present but one representative ; the second Family 
contains sixty-seven species. I have, however, been unable to classify them in a satis- 
factory manner, chiefly because, as has been already mentioned, the state of preservation 
of many of the individuals rendered it impossible to make out with any certainty the 
structure of various organs important for systematic purposes. I could not, for example, 
ascertain whether all the free-living species were really hermaphrodite, as I should have 
been obliged to destroy several unique specimens in order to determine whether the testes 
were present or not. If this point had been placed beyond a doubt, I should have divided 
the second Family into two groups — (a) hermaphrodite forms ; (b) dioecious forms. In the 
same way with many other secondary characters, — such as the presence or absence of 
suckers, the m.uscula,r septa, &c., — it was impossible to make a thorough investigation. 
The following Table of Species, therefore, is given only for use in the determination 
of species. No doubt when more abundant material has been examined it will be 
possible to give a generic sub-classification of the Family Myzostomidse. 
Table of Species. 
***** 
I. With ramified intestinal canal. Family Myzostomidse, genus Myzostoma. 
* F ree-living, not forming cysts (mostly with, suckers). 
* * Mouth terminal or ventral. 
* * * Without caudal appendages. 
* * * * With distinct suckers. 
Border of the disk quite smooth. 
Border of the mouth covered with papillae, 
Border of the mouth without papillae. 
Back with radial series of hard tubercles, 
Back without tubercles. 
Parapodia long, placed near the border. 
Back two-coloured, .... 
Back one-coloured. 
Skin of the back light yellow, with tubercles, 
Skin of the back grey-brown, areolated, 
Parapodia short, nearer to the centre, 
Border of the disk irregularly toothed. 
Body oblong, extended, with few obtuse ribs, 
Body circular. 
With numerous sharp-edged ribs, 
With numerous obtuse ribs, .... 
* * * * 
M. labiatum. 
M. echinus. 
. M. horologium. 
. M. longipes. 
M. chinesicum. 
M. alatum. 
. M. rubrofasciatum. 
M. plicatum. 
. M. costatum. 
