76 THE VOYAGE OF H.M.S. CHALLENGER. 



Planulse were not examined in the fresh condition, hence the ciliation of their 

 surface, doubtless occurring, was not observed. In the most mature planula investi- 

 gated, the endoderm consisted of pigmented cells, like those of the endoderm of the 

 mature coral, but evidently in a condition of rapid increase, and of oil-globules of 

 various sizes and fine granular matter. The endoderm mass did not show any trace 

 of a central cavity, but appeared homogeneous and solid. The gonophore sacs seem 

 to be permanent in Cryptohelia pudiaa, and the production of planuke within them to 

 be carried on as a continuous process. 



Growth by Budding. — In ordinary growth of the coral by budding, every part of the 

 coral surface would appear capable of producing complete cyclo-systems, for in one 

 specimen procured a new cyclo-system has been abnormally produced as a bud from 

 the upper surface of the lid of an older cyclo-system. 



General Bemarks on the Structure of the Stylastertd^e. 



Summaries of the characteristics of the sub-order HydrocorallinEe and its subdivisions 

 will be given in the secpiel under the heading " Classification." A few further special 

 points in the structure of the family of the Stylasteridse require to be noted here. The 

 Hydroid affinities of the Stylasterida? need no discussion ; they are borne out by every 

 item of structure. 



As in almost all Hydroids, the sexes are on distinct stocks, and these stocks, like 

 those of Sertularians, have a tendency to grow in a flabellate form with alternate 

 gemmation. In having the numbers of the tentacles borne by the gastrozooids regular 

 in number in each species, possibly in each genus, the Stylasteridaa differ from the 

 Milleporida3, in which the number is variable. The connection of an absence of the 

 styles in the gastropores with a flask-shaped form of gastrozooid devoid of tentacles is 

 remarkable. It occurs in apparently otherwise widely separated genera, Astylus and 

 Pliobothrus. It is possible that the tentacles of the gastrozooids in all the genera 

 would show traces at least of having knob-like or club-shaped ends were they examined 

 in the fresh condition. 



The gonophore sacs within the ampullae, as containing several distinct gonophores, 

 in several genera at least, seem entitled to the term " gonangia," according to 

 Allman's terminology. It seems uncertain whether the central mass in Astylus, 

 from which the sperm-developing lobules are budded off, is to be considered as a 

 blastostyle or not ; no definite spadices were observed within these lobules. 



The radiate arrangement of the ccenosarcal canals around the sacs of the zooids, 

 which is so remarkably developed in Sporadopora and Allopdra, and traces of which 

 appear in nearly all the genera, is very remarkable. It gives the soft structures of 

 Allopora, at first sight, a still closer resemblance in arrangement to that occurring 



