1897-98.] Dr Masterman on Archimeric Segmentation. 283 
with that of the trochosphere. Allowing for the alterations due to 
a long period of burrowing habit and the consequent adaptations, 
the anatomy of Balanoglossus is very close to that of the ancestral 
type. 
Cephalodiscus {Deep-Sea). 
The great anatomical resemblance to Balanoglossus* is well 
known, and we need only note here 
that in this form the subneural gland 
is functional, and retains its primitive 
connection with the stomodseum. The 
persistence of mesomeric tentacles pre- 
oral in position, and of a reflexed 
alimentary canal, can be traced to the 
semi-sedentary habit, and the reten- 
tion of the protomere and hypertrophy 
of the pedicle (or ventral sucker) to 
its peculiar mode of locomotion and 
attachment. 
Fig. 3 shows the young form in hori- 
zontal section, with the five archicoeles. 
We have only to add that, as in Fig. 3.— Diagrammatic hori- 
D 7 7 , n it zontal section through 
Balanoglossus , the protoccelic pores n 7 7 7 . & 
r young Cephalodiscus. 
(proboscis-pores) and mesocoelic pores 
(collar -pores) are functional, and the metacoelic pores are purely 
gonaducal. 
Brachiopoda {Sedentary). 
In this archaic group there is no indication of true metameric 
segmentation. The presence of two pairs of nephridia in Rhyn- 
chonella cannot be regarded as such, for, apart from other consider- 
ations, the archimeric segmentation allows of two pairs of post-oral 
segments. 
The external form of the Brachiopoda is profoundly modified 
by the sedentary habit of the group, so that the most striking 
evidence for its claims to be regarded as a division of the Archi- 
* S. F. Harmer, Challenger Reports , vol. xx., and A. T. M., Q. J. M. S., 
August 1897. 
