GENERAL MORPHOLOGY OF THE BODY. 
Form of the Body. 
All the Myzostomida hitherto known are characterised by the peculiar radial arrange- 
ment of the organs of the body. Corresponding to its disk-like form, we find the ten para- 
podia situated at pretty equal distances from each other, so that the whole body is divided 
into ten regular “ parapodial sectors on the boundary lines between each of these are 
the eight suckers, the oral and the cloacal apertures. The sectors are separated inside the 
body by an equal number of radially arranged muscular septa, which thus form a number 
of similar compartments. The same radial arrangement is seen in the muscles of the 
hooks, especially in the strong musculi centrales, which unite in the middle of the body 
in a large muscular mass. In certain species where the axis of the body becomes length- 
ened, and so disturbs the circular arrangement of the suckers and parapodia, the radial 
character is nevertheless retained by the compartments, each corresponding to a single 
parapodium. 
In the present Report several species will be described in which this radial arrange- 
ment is entirely lost ; in some cases ( Myzostoma folium ) the body is greatly lengthened 
and the parapodia and suckers are situated in two parallel lines, while in the new genus 
Stelechopus not only has the external radial symmetry disappeared, but the muscular 
septa and the muscles of the parapodia are no longer convergent. In Stelechopus the 
septa are situated one behind the other at right angles to the axis of the body, running 
from the body-wall to the intestine, and the parapodia show the same bilateral symmetry, 
and their muscles are not united into a central muscular mass (PI. XVI. fig. 1). If, 
as I have already 1 tried to prove, the radial arrangement of the musculature is indeed an 
adaptation to the mechanism of fixation, the want of this radial arrangement in Stelechopus, 
which undoubtedly moves about freely, must be regarded as the primitive arrangement. 
Myzostoma glahrum has been until now the only exception to the general rule that 
the apertures of the body, as well as the parapodia and suckers, are situated upon its 
ventral surface ; in this species the cloacal aperture is dorsal. I shall have in the present 
Report to describe two new species ( Myzostoma pulvinar and Myzostoma calycotyle) in 
which the oral and cloacal apertures are upon one side of the body, while the parapodia and 
suckers are upon the other. If the parapodia alone be not sufficient to determine that 
1 Loc. cit., p. 44. 
