THE ORTHONECTIDA. 
225 
The Orthonectida, a New Class of the Phylum of the 
Worms. ^ By Alfred Giard^ Professor in the Faculty 
of Sciences of Lille. With Plate XXII. 
In 1868, in an interesting memoir^ on the -marine Plana- 
rians of St. Malo, Keferstein figures an animal which he 
designates by the name problematic parasite.” The ex- 
planation of the plate (plate ii, fig. 8) indicates that this 
parasite has been found several times, and often in great 
quantity, in the digestive tube of the Tremellaria (Lepto^ 
plana tremellaris). The text gives us no information as to 
this curious organism, and it is chiefly by means of the 
rather rough figure of the second plate of Kerferstein's work 
that we are led to refer it to the group which we are about 
to study. 
Macintosh, in his beautiful monograph of the British 
Nemerteans, published in 1874,® recalls the observation of 
Keferstein in reference to a parasite which he met with in 
Linens gesserensis {Nemertes communis of P. J. Van 
Beneden), and concerning which he gives the following 
details, accompanied by a few drawings : 
“ Another curious parasite is found burrowing in the body- 
wall of Linens gesserensis, its presence being readily recog- 
nised by the perforated and honeycombed appearance of the 
dorsum of the affected animal, whose textures seem to be the 
seat of the workings of a microscopic Tomicus typographicus. 
When highly magnified, the afiected region appears to be 
covered with a vast network of pale, minutely granular 
channels, which contain numerous opaque, ovoid, granular 
masses. 
On rupturing the body of the worm a large number of 
the peculiar structures (plate xviii, fig. 17) slide out of the 
channels, and swim through the surrounding water, generally, 
though not always, with the upper end (in the figure) first. 
Externally they are coated with long cilia, whose activity in 
the free state is of somewhat short duration, for after a time 
the animals remain quiet, and they drop off. The body is 
^ This memoir has been corrected and new matter, including pre- 
viously unpublished figures, has been added by Professor Giard to the 
original memoir, which appeared in ‘ Robin and Ponchet’s Journal,’ for 
the present publication. 
’ keferstein, ‘Beitrage zur Anatomic und Entwickel. einiger See- 
planarien,’ Gottingen, 1868. 
3 ‘A Monograph of the British Annelids,’ part i, Ray Society, p. 129, 
and pi. xviii, ngs. 17, 18, 19. 
