146 



MANUAL OF ZOOLOGY. 



often of large size, and which have been generally referred to 

 the Corals (Actinozoa). One of these groups comprises the 



well-known Millepora (fig. 64), 

 which is found contributing so 

 largely to the formation of coral- 

 reefs in the West Indies and 

 Pacific. The calcareous skeleton 

 of Millepora is mostly in the form 

 of foliaceous or laminar expan- 

 sions, stony in texture, with a 

 smooth surface studded with rni- 

 nute apertures of two sizes, the 

 larger of these being much the 

 fewest (fig. 64, C). The larger 

 openings are the mouths of tubes 

 (fig. 64, B,^/), which are divided 

 by transverse calcareous parti- 

 tions into a number of compait- 

 ments, only the most superficial 

 of these being actually tenanted 

 by the living animal. The smaller 

 tubes are similarly septate or 

 "tabulate," and the general tis- 

 sue of the skeleton (fig. 64, C) 

 is composed of calcareous tra- 

 beculae traversed by a series of 

 ramifying and anastomosing coe- 

 nosarcal canals, which place the 

 tubes occupied by the zooids in direct communication. 



From the presence of transverse partitions, or " tabulae," in 

 its tubes, Millepora was generally placed amongst the 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 ob- 

 served. The late Professor Agassiz was the first to examine 

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

 sion that the genus was unequivocally referable to the Hydro- 

 zoa. A similar conclusion has recently been reached by Mr 

 Moseley, who had the opportunity of examining the living 

 animal minutely. According to this observer, the colony (fig. 

 65) of Millepora consists of two kinds of zooids. The larger 

 zooids, or " gastrozooids," inhabit the larger tubes of the skele- 

 ton, and possess from four to six knobbed tentacles ; while the 

 smaller zooids, or " dactylozooids," inhabit the smaller tubes, 

 and are either indiscriminately mixed with the gastrozooids, or 



Fig. 63. Di A 



nidian Grapt 



<tus pristis, a diprio- 

 te. (Original.) 



