THE MORPHOLOGY OF THE CHFJLOSTOMATA, 



321 



from those of the ordinary individuals of the colony. This, 

 the primary zooecium, has been termed the " ancestrula " by 

 Jiillien (1888, 4, pp. 27, 29), a name wliich he appears to 

 have used merely to convey the idea that it was the actual 

 ancestor ("zooecie mere") of the other individuals of the 

 colony. Smitt (1868, 1, p. 306) described the same thing as 

 the " Tata form " of the Cheilostomes,^ and clearly recognised 

 their importance, stating that ''Tata is for the Cheilostomes 

 what Alec to showed itself to be for the Cyclostomes." 



I am fully of Smitt's opinion with regard to this matter. 

 The '^ancestrula" is in all probability ancestral in the sense 

 of retaining characters of phylogenetic importance. Smitt 

 returns to the same subject in a later publication (1896), in 

 which he again maintains the importance of the Tata form. 

 Neviani (1898, p. 165) supports the same conclusion. 



The frequency Avitli which the Tata-like ancestrula (figs. 

 2, 6, 7) occurs in Cheilostomata is indeed remarkable, and 

 there is a curiously small range of variation in the number of 

 its marginal spines. I subjoin a few references to cases 

 where an ancestrula of this type has been described. 



' The young zncecia figured as Tata rugosa by Van Beneden (' Bull. 

 Acad. Roy. Belgiqiie,' xvi, pi. ii, fig. 14) are primary zooecia of a ]\Ifm- 

 branipora. 



VOL. 46, PART 2. — NEW SERIES. W 



