REPORT ON THE ANTIPATHAIUA. 67 



.simple base. In this way a double spine (V-shaped) is formed, and later, by a continual 

 increase in the thickness of the sclerenchyma, the originally simple spine becomes con- 

 verted into two, which at first are recognisable on account of their close proximity, but 

 which tend to become more and more isolated. It will thus be seen that drawings of 

 the spines, in order to be of value in the identification of species, must be taken from 

 certain more or less limited areas. On this account many of the drawings of Pourtales 

 are not satisfactory, because they represent the arrangement at the apex of a branch, 

 where, as already stated, the specific features of the spines have not yet been assumed. 

 In most Antipathidse with moderately long pinnules it is necessary to pass over half an 

 inch at any rate before the normal characters obtain regularity. In the illustrations of 

 the arrangement of spines accompanying the present Report, I have, wherever possible, 

 examined a branch or pinnule from the apex downwards, selected an area which seemed 

 to have "normal" spines, and then finally figured that portion of it which seemed to 

 show T best the arrangement of the spines on the axis. All are drawn to scale, and the 

 details have been filled in by the aid of an eye-piece micrometer. The amplification is 

 always given, and this should be borne in mind for purposes of identification, as it gives 

 a clue to the diameter of the axis, — an important point in such cases. 



Retrogressive Development. 



The life-history of a zooid may be divided into two cycles, the one a progressive 

 metamorphosis and the other a gradual retrogression leading to atrophy. It appears, 

 however, that the retrogressive changes do not affect all species in the same way. In the 

 Schizopathinse, where new zooids are usually added at the apex of a branch, the first signs 

 of retrogression are frequently to be found at a point some distance above the base. 

 This consists at first in a greater isolation of the individual zooids. It sometimes 

 happens, as in Schizopathes affinis (PL IX. fig. 2), that only the terminal portion of a 

 branch presents the normal arrangement of zooids. In the lower portion the zooids 

 gradually become more and more isolated, and at the same time the body of the zooid 

 becomes so much reduced, that before the base of a branch is reached, all that remains is 

 a pair of tentacles projecting beyond the ccenenchyma; these appear to retain their 

 original form for a very long time. In other cases (e.g., Schizopathes crassa) the 

 individual zooids appear to remain functional for a longer period, and the retrogression 

 may only be observable on the stem and basal portion of the colony. In Schizopathes 

 and Bathypathes, however, the body of the zooid always appears to be lost first, and the 

 tentacles remain for a considerably longer period to indicate its position. In the Anti- 

 pathinse the retrogressive changes take a different course. In many species the formation 

 of new zooids as buds from the stolon-like out-growth of the ccelenteron of an adult, keeps 

 up the supply of functional zooids in a given area for a longer period than would other- 



