812 KECORD OF CURRENT RESEARCHES RELATING TO 



The results of the paper may be summarized thus : — 



(1) Foundations have been prepared for barrier reefs and atolls by 

 the disintegration of volcanic islands, and by the building up of sub- 

 marine volcanoes by the deposition on their summits of organic and 

 other sediments. 



(2) The chief food of the corals consists of the abundant pelagic 

 life of the tropical regions, and the extensive solvent action of sea- 

 water is shown by the removal of the carbonate of lime shells of these 

 surface organisms from all the greater depths of the ocean. 



(3) When coral plantations build up from submarine banks, they 

 assume an atoll form, owing to the more abundant supply of food to 

 the outer margins, and the removal of dead coral rock from the 

 interior portions by currents, and by the action of the carbonic acid 

 dissolved in sea-water. 



(4) Barrier reefs have built out from the shore on a foundation of 

 volcanic debris, or on a talus of coral blocks, coral sediment, and 

 pelagic shells, and the lagoon channel is formed in the same way as a 

 lagoon. 



(5) It is not necessary to call in subsidence to explain any of the 

 characteristic features of barrier reefs or atolls — all these features 

 would exist alike in areas of slow elevation, of rest, or of slow 

 subsidence. 



(6) All the causes here appealed to for an explanation of the 

 structure of coral reefs are proximate, relatively well known, and con- 

 tinuous in their action. 



New Mode of Reproductioii among the Hydroida,* — Dr. Goette 

 describes the structure and history of a new species of Hydroid- 

 polyp, which he discovered on a Campanularian during his recent 

 visit to Naples ; he calls it Hydrella ovipara, and describes it as 

 having a creeping stolon which bears here and there simple branches, 

 which are scarcely 1 mm. in length, and terminate in a hydranth. A 

 skeletal tube, irregularly annulated at its base, invests the body, but 

 does not form a proper hydrotheca. Remarkable stages were observed 

 in the characters of the stalk, which was in some cases completely 

 atrophied at its middle, so as to be reduced to a thin filament, and to 

 be comj^osed only of the ectoderm. It would appear that H. ovipara, 

 like some other Hydi'oids (e. g. Eudendrium), undergoes a degeneration 

 of some of its polyps at the period of sexual maturity ; the ova are 

 developed from endodermal cells, and within the stalk ; here the eggs 

 undergo their further development, instead of being conveyed into a 

 gonophore, while the remaining i)art of the neighbouring endoderra 

 undergoes atroj^hy. These observations are sufficient to demonstrate 

 that there is no polymorphism and no alternation of generation in this 

 species. With this we should note the fact that in many species of 

 Lafoeida no alternation has yet been detected, and it is possible that 

 there is none to be observed. 



Forms a little more distant, e. g. CordylopJiora, exhibit an incom- 

 plete development of this alternation of generation, ova being deve- 



* 'Zool. Anztig.,' iii. (1880) p. 352. 



