148 MANUAL OF ZOOLOGY. 



series of large apertures, with more numerous and irregularly 

 distributed smaller openings, the latter not being radially ar- 



Fig. 65. Enlarged view of a portion of the surface of a living colony of Millepora 

 nodosa, showing the expanded zooids of a single system : a Central "gastrozooid ; " 

 b One of the mouthless " dactylozooids." (After Moseley.) 



ranged round the former. In any case, the skeleton is tra- 

 versed in all directions by a system of branched and anasto- 

 mosing canals, which are occupied in the living condition by 

 prolongations of the ccenosarc, which also forms an ectodermal 

 covering to the skeleton. The colony is composed of two 

 different sets of zooids the one set (" gastrozooids ") provided 

 with a mouth and stomach-sac; while the others ("dactylo- 

 zooids") are elongated and destitute of a mouth, thus coming 

 to represent tentacles in form. The gastrozooids occupy, as in 

 Millepora, the large tubes of the skeleton, and the dactylo- 

 zooids, are lodged in the small tubes. Hence, when the dac- 

 tylozooids are arranged in definite " cyclo-systems " round the 

 gastrozooids, then each of the large apertures in the skeleton 

 comes to be surrounded by a circle of smaller elongated pores, 

 which are only separated laterally by thin partitions, and which 

 thus give rise to the appearance of a central "calice" sur- 

 rounded by radiated "septa" (fig. 66, B). The gastrozooids 

 are not only larger than the dactylozooids, but they have a 

 special layer of digestive cells lining the' body-cavity, a struc- 



