FOSSIL HYDROZOA. 



171 



West Indies and Pacific. The calcareous skeleton of Mille- 

 pora is mostly in the form of foliaceous or laminar expan- 

 sions, stony in texture, with a smooth surface studded with 

 minute apertures of two sizes, the larger of these being much 

 the fewest (fig. 65, c). The larger openings are the mouths 

 of tubes (fig. 65, B, p, p), which are divided by transverse 

 calcareous partitions into a 

 number of compartments, only 

 the most superficial of these 

 being actually tenanted by the 

 living animal. The smaller 

 tubes are similarly septate or 

 "tabulate," and the general 

 tissue of the skeleton (fig. 65, 

 c) is composed of calcareous 

 trabeculae traversed by a series 

 of ramifying and anastomos- 

 ing coenosarcal canals, which 



place the tubes occupied by 

 the zooids in direct commu- 

 nication. 1 



From the presence of trans- 

 verse partitions, or "tabulse," 

 its tubes, Millepora was 



in 



Fig. 64. Group of individuals of Phyllo- 

 graptus typus, from the Quebec group of 



.. Canada (after Hall). One of the four rows 



generally placed amongst the of cells is hidden on the under surface. 



so-called "Tabulate Corals," 



with the typical forms of which it has no affinity. Though 

 its skeleton is abundantly obtained in the regions where 

 it occurs, the living animal has been rarely observed. 

 The late Professor Agassiz was the first to examine 

 Millepora in its living condition, and he was led to the 

 conclusion that the genus was unequivocally referable to 



1 As regards the living animal, Mr Moseley has shown that the colony of 

 Millepora consists of two kinds of zooids, differing in size, in structure, and 

 in function. The larger zooids occupy the larger tubes of the corallum, and 

 have a mouth, surrounded by four tentacles and opening into a digestive 

 cavity. The smaller and more numerous zooids surround the larger ones, are 

 long and slender in form, carry numerous clavate tentacles, and are destitute 

 of anj r mouth. They perform the functions of prehension for the colony, and 

 supply food to the nutritive zooids. 



