392 EIGHTH PACIFIC SCIENCE CONGRESS 



fossil forms of the Tertiary Period show striking resemblances to the 

 recent species, the palaeogeography of the Region will be effectually 

 traced back to the Tertiary or the Cretaceous Period. Text-figures pre- 

 sent the geological history of the Indo-Pacific Region. 



In the Upper Cretaceous and the Eocene, the northern Pacific 

 Ocean was isolated from both the Indian Ocean and the Antarctic Sea, 

 and conspicuously narrowed. The southern half of the Pacific was 

 made afterwards by the secondary fusion of the northern half and the 

 Antarctic. During the Eocene, Oligocene and Miocene epochs, the In- 

 dian Ocean was connected with the Mediterranean Sea by one or two 

 ways. The Ethiopian Sea was recognized connecting the Mediterra- 

 nean and the Indian Ocean along the African coast. 



In the Upper Eocene, the Pacific Ocean found the way to the In- 

 dian Ocean by a newly opened passage at the Malayan coast. The 

 north Australian coast was formed nearly at the same epoch. The 

 above-mentioned history of the Indo-Pacific Region suggests to us the 

 possibility of the following areas significant to the specific differentia- 

 tion: 1) The northern Pacific. 2) The southern Pacific. 3) The east- 

 ern coast of Africa. 4) The northern part of the Indian Ocean. 



OCEANOGRAPHICAL AND ECOLOGICAL FACTORS 



Larvae: So far as we are aware, one of the most characteristic fea- 

 tures of the Bryozoan colonies is their sessile habit of growth. The dis- 

 tribution of the individual colony is, therefore, accomplished only by 

 the dispersion of minute larvae within their short swimming period of 

 a day or two. The colony attaches to various sorts of substrata such 

 as rocks, stones, sand grains, sea-weeds, sponges, hydrozoon stems, sea- 

 urchins, worm tubes, brachiopod shells, bivalves, gastropod shells, other 

 bryozoans, lobsters, crabs, and ascidians. The secondary dispersion is 

 affected by gastropods or lobsters carrying bryozoans on them. The 

 migration along the coast-lines proceeds thus. 



The Cyphonautes, a specialized form of bryozoan larvae, is able to 

 continue their swimming life of several weeks, thus extending their 

 range with much ease. 



Ocean Current: In addition to migration along the coast-lines, 

 there has been a more irregular and sporadic diffusion by the agency 

 of currents, floating sea-weeds, drifting woods and by means of ships. 

 Wide distributional range of some species which produce Cyphonautes 

 larvae or take their residence on sea-weeds, might be caused by the 

 action of currents. 



As is well known the Pacific Ocean is divided into two, the northern 

 and the southern half, from the oceanographical standpoint. The North 



