TRANSACTIONS OP SECTION D. 433 



the starfish has similar relations with the right and the posterior aspects of the 

 larva. Definite sequence in formation of hydrocele lobes. Mode of numbering 

 the lobes. Archenteron ultimately divides into anterior, middle, and posterior 

 chambers. The middle chamber gives rise to the gut, the development of which 

 histologically and otherwise may be said to be post-dated. The posterior cham- 

 ber gives rise to the hypogastric and pharyngeal cceloms, to all but segment IX /I 

 of the external oral circular sinus, to the genital pocket and cavity of aboral 

 circular sinus. The anterior chamber gives rise to the rest of the typical series 

 of internal cavities. As regards skeleton, two terminals appear at the tip of 

 each arm rudiment, while the first aboral plates are numerous and distributed 

 without reference to radii and interradii. Anus develops in interradius V/VI. 

 A larval nervous system and a statolith-like body. Early growth and habits of 

 the young Solaster. Methods employed to rear them at the Millport Marine 

 Station. 



5. Remarks on some of the Boring Mollusca. 

 By W. T. Elliott, F.Z.S., and B. Lindsay. 



A theory has been put forward, at various times and in various forms, that 

 the work of marine boring organisms is performed by means of an acid secretion. 



In the saliva of predatory shell-piercing Gasteropods an acid really exists. 

 This, in the Sting-winkle, has been studied for the sake of comparison, but the 

 presence of acid secretion in the head of a Gasteropod affords no presumption 

 that it may occur in the foot of a mollusc of another class. 



Observations on the boring marine organisms of the shore at St. Andrews con- 

 firm the statement of Professor Mcintosh that their method of boring is mecha- 

 nical and not chemical. No acid secretion was detected at any time. 



Zirphaa (Pholas) crispata and Saxicava rvgosa both work by , means of 

 vacuum-suction, supplemented by scraping movements of the shell, which in the 

 former are continuous and purposeful during the time of boring. Vacuum- 

 suction is created by co-operation between the mantle and the foot. The part 

 played by the folds of the mantle is indicated by the structure of the shell in 

 Ztrpliaa. 



The common limpet, when on sandstone, works for itself a shallow depression 

 in a similar way by suction assisted by shell-scraping movements, but the latter 

 are not purposeful. It does not succeed in making any depression in harder 

 rocks. 



The boring molluscs are not singular among boring organisms in working by 

 mechanical means. The annelid Polydora ciliata, very common at St. Andrews, 

 also does so, and is typical of boring annelids in its method of procedure. It 

 wears away the substance in which it works by the muscular action of a coil of 

 its body ; often fixing its head so as to use it for a fulcrum, and sometimes using 

 the tail' in a similar way, by means of the terminal suction-cup. 



The boring of these and other organisms probably has an important bearing 

 on coast erosion. At St. Andrews the boring-grounds exist in close proximity to 

 instances of sea encroachment, and the same fact may be observed near Black- 

 pool in Lancashire and in the chalk cliffs near Brighton. 



6. Discussion on Wallace's Line. Opened by C. Tate Regan, M.A. 



The distinguished naturalist, Alfred Russel Wallace, spent several years 

 (1854-62) in the Malay Archipelago, making zoological collections and studying 

 the islands and their inhabitants; he came to the conclusion that the islands 

 should be grouped in two main divisions : an Indo-Malayan, comprising Borneo, 

 Sumatra, Java, with Bali and the Philippines, and an Austro-Malayan, including 

 New Guinea, the Moluccas, Celebes and the islands from Lombok to Timor. 



The line separating these two divisions has long been known as 'Wallace's 



Line,' and for many years was generally accepted as the boundary between the 



Oriental and Australian Zoegeographical Regions. This view has lately lost 



ground considerably, and some zoologists now include Celebes and the Timor 



1911. F F 



