REPORT ON THE ANTIPATHARIA. 



63 



similar in other colonial Zoantharia, but in Madreporaria is apparently more complex, 

 due, doubtless, to a lack of regularity in the position of the blastozooids and to the 

 modifications necessitated by the presence of a calcareous exoskeleton. In Leiopathes 

 glaberrima, for example, the zooids are frequently separated from each other by a 

 considerable interval ; they are irregular in size, and a close examination shows that very 

 young ones are scattered here and there, which are only recognisable as slight rounded 

 prominences, without a mouth or tentacles ; others show a depression in the centre of the 

 prominences, and those still further advanced show the rudiments of tentacles. In 

 transverse vertical sections the zooids are seen to be connected together by tubular out- 

 growths of their ccelentera, running along the axis of the branch between the zooidal 

 tissue proper and the cellular sheath of the sclerenchyma. The zooids are imperfectly 

 separated from one another by vertical mesoglceal partitions which do not reach the 

 sheath of the sclerenchyma, thus leaving a free communication between the ccelentera of 

 adjoining zooids. In such sections passing through a very young zooid the elevation of 

 the surface ectoderm, which indicates the position of the new zooid, is seen to correspond 

 with a dilation in the ccelenteron. This ddation is situated in the narrow lateral out- 



Fig. IS. — Diagram of the formation of new zooids by means of buds (Leiopathes). 



growth, passing on to the next adult zooid, and at a point not far from the mesoglceal 

 partition separating the tissues of the two adults. A diagrammatical representation of the 

 arrangement is shown in fig. 18. In Leiopathes apparently a new zooid may be added 

 at any point along the branch, its ccelenteron being at first a dilation of that of one of 

 the adults. This type of budding gives rise to great irregularity in the size of the indi- 

 vidual zooids on a branch. Sometimes large and small zooids appear to alternate with one 

 another, but more usually the sequence is irregular. Pourtales called attention to this 

 feature in Leiopathes glaberrima (cf. PI. IV. fig. 9). I have noticed it also in Antipathella 

 subpinnata and other forms, but it appears most marked in Leiopathes. In Antipathdl" 

 subpinnata the zooids in the basal two-thirds of a branch are usually very regular in 

 size, the new zooids being apparently introduced chiefly between zooids of the newer 

 portion of the colony. In the unbranched species Stichopiathes pourtalesi, according to 

 the observations of Pourtales, large and small zooids alternate with considerable 

 regularity. Ova were observed in the large ones, and Pourtales suggests that the smaller 

 ones may differ in sex. In all the species of Antipathidaa I have yet examined the zooids 



