538 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
with the epiblast. At the same time as this growth in length takes 
place, the cells undergo a remarkable modification into vacuolated tissue. 
After comparing Actinotroclia with Balanoglossus and with Tornaria , 
the author sums up his views in this classification : — 
Chordata. 
I. Archichordata. 
Archimeric segmentation into protomere, paired mesomeres, and 
metamere ; little or no metameric segmentation. Notochord in primitive 
continuity with the walls of the gut throughout life. More or less con- 
nected with the protomere, the main animal organ of the body. Nerve- 
ganglion between protomere and mesomere, or dorsal to mesomere. 
Main nerves are protomeric ring, mesomeric ring, and dorsal and ventral 
trunks. A mesoblastic chondroid skeleton and an ectodermal chitinoid 
tube or skeleton. 
(1) Hemichorda. Notochord fused in middle line and protruding far 
into the protomere. Commencing metameric segmentation in gill-slits 
and gonads. 
(2) Diplochorda. Notochord in primitive paired condition. In close 
connection with the two posterior protomeric mesenteries. Mesomeres 
produced into numerous tentacles. Metameres with dorsal flexure. 
Phoronidea (loss of pre-oral lobe and notochord in adult ; no gill- 
slits). Cephalodiscida (one pair of gill-slits with chordoid walls ; per- 
sistent notochords). Rhabdopleurida. 
II. Eu-chorda. 
Archimeric replaced by metameric segmentation. Single dorsal noto- 
chord loses connection with gut-wall, and dorsal nervous system with the 
ectoderm. Protomere and mesomeres reduced. Notochord extends into 
metamere (Urochorda, Holochorda), and also into protomere (Cephalo- 
chorda). 
(1) Urochorda (?) (2) Cephalochorda. (3) Holochorda. 
Structure of Cephalodiscus.* — Mr. A. T. Masterman has had the 
privilege of re-investigating this rare animal. His preconceived view 
that Harmer’s “ notochord ” is the homologue of the subneural gland, 
and that Cephalodiscus has a paired notochord, has been confirmed to a 
remarkable degree. He proposes to include Balanoglossus , Cephalodiscus , 
and Phoronis in one group (Archichorda), the first being hemichordate, 
the two others diplochordate. His definition of the Diplochorda (the 
name expresses one of the author’s main positions) reads as follow's : — 
Mesomeres produced laterally into a number of ciliated branchial 
tentacles, which in the adult point upwards in front of the mouth, are 
supported by a chondroid skeleton, and subserve ingestion of food. 
Metameres reduplicated by a dorsal flexure. Stomodaeum with subneural 
gland still opening to the exterior, and extending into the subneural 
sinus. Paired proboscis-pores near median dorsal line, arising internally 
along the wall of the subneural sinus. Paired notochords in pharynx 
not displaced forwards. A short oesophagus, stomach, and intestine. 
One pair of pharyngeal clefts may ( Cephalodiscus ) or may not ( Bhabdo - 
* Quart. Journ. Micr. Sci., xx. (1897) pp. 340-66 (4 pi?.). 
