1897-98.] Dr Masterman on Archimeric Segmentation. 287 
forms, all showing a well-marked segmentation into one pre-oral 
and two post-oral segments. The pre-oral portion or protomere 
appears to become the epistome of the adult,* whilst the mesomere 
Fig. 9. — Larval Argiope 
(after Shipley). 
Tig. 10. — Later larval Argiope 
(Kowalevski). 
becomes the lophophoral cirrhi and the mantle lobes, into which 
the metacoelic cavities are later produced. This segment, as in 
Annelida , hears provisional setse (m.s., figs. 10 and 9). To this we 
may add that the mesoderm arises by archenteric diverticula. 
Fig. 11. — Larval Thecidium (after 
Lacaze-Duthiers). 
Fig. 12. — Larval Terbratulina 
(after Morse). 
There are two difficulties to he mentioned. The coelomic pouches 
have not been described as breaking up into four archicoeles, and 
hence the larval segments are not considered as segments by some. 
* Cf. Korschelt and Heider, loc. cit., p. 1238, fig. 720. 
