4o6 



NATURE 



[December io, 1914 



Dath. The simplest explanation of the distribution of 

 narsupials, past and present, is that they originated 

 n South America, spread by way of Archihelenis to 

 kvestern Europe, by way of the West Indies to North 

 \merica, and by way of Antarctica to Australasia, 

 fuming to the Amphibia, Mr. Hedley pointed out 

 :hat the families Hylidae and Cystignathidae have their 

 ihief seat in South America, and both families extend 

 :o Australasia, where they are best developed in the 

 south-east and gradually vanish before reaching the 

 Moluccas. In these cases also the most direct route 

 Detween the two centres lies across Antarctica, and 

 Dy cumulative evidence from plants and animals of 

 Tiany and varied kinds the conclusion is reached that 

 :his was the way they went. 



Prof. Seward gave a brief account of some of the 

 fossil plants collected by members of Captain Scott's 

 second expedition, with special reference to Dr. \^'il- 

 son's discovery of Glossopteris in 85° S. Fragments 

 3f well-preserved leaves of Glossopteris indica found 

 in the rocks of Buckley Island, a nunatak on the 

 Beardmore Glacier, afford important evidence, both 

 as to the age of the Beacon Sandstone formation and 

 as to a former connection between Antarctica and 

 Gondwana Land. The geological distribution of 

 Glossopteris in other parts of the world suggests that 

 the strata of the Buckley nunatak must be assigned 

 to the Permo-Carboniferous period. A large piece of 

 wood obtained by Mr. Priestley from a sandstone 

 boulder on the Priestley Glacier in 74° S. proved to 

 be a gymnospermous stem of considerable botanical 

 interest ; the wood shows well-marked rings of growth 

 and exhibits Araucarian characteristics, but in view 

 of certain peculiar features has been referred to a 

 new genus — Antarcticoxylon. Associated with this 

 was found a winged pollen-grain, described as Pityo- 

 sporites, which bears a striking resemblance to the 

 pollen of recent Abietineae. In conclusion, Prof. 

 Seward referred to the bearing of these important 

 discoveries on climatic considerations, and pointed out 

 that while there is clear evidence of a considerable 

 change in climatic conditions since the period when 

 Glossopteris flourished on the Antarctic continent, 

 there is no adequate reason to assume any change 

 in the position of the earth's axis. Meagre as it is, 

 the material collected by the polar party calls up a 

 picture of an Antarctic land on which it is reasonable 

 to believe were evolved the elements of a new flora that 

 spread in diverging lines over a Palaeozoic continent, 

 the disjuncta membra of which have long been added 

 to other land-masses where are preserved both the 

 relics of the southern flora and of that which had its 

 birth in the north. 



Plankton. 



Prof. Herdman gave an account of some recent 

 plankton investigations in European seas (especially 

 in the Irish Sea and off the west coast of Scotland), 

 and of the apparatus used and the difficulties met 

 with. He exhibited photographs of different samples 

 of hauls showing that the diatoms attain their maxi- 

 mum in spring and are at a minimum in summer, 

 while the copepods are few in spring but numerous 

 in summer. He pointed out the necessity for taking 

 samples simultaneously with vertical and horizontal 

 nets, and for using coarse and fine nets in order to 

 gain a true picture of the total plankton, and referred 

 to the irregularity in distribution of plankton organ- 

 isms, swarms of organisms being sometimes present 

 in restricted areas, hence it was necessary to be care- 

 ful in drawing conclusions from the samples taken in 

 a single haul. He briefly discussed the application of 

 plankton investigations to fishery problems, pointing 

 out that diatoms are the ultimate food of marine 



NO. 2354, VOL. 94] 



animals, and therefore the starting-point of the 

 problems. 



The Abrolhos Islands. 



Prof. VV. J. Dakin gave a summary of some of the 

 results of recent work by himself and Mr. W. B. 

 Alexander on the Abrolhos Islands. These are 

 situated in lat. 28° 40' S., about fifty miles off the 

 west coast of Australia, and near the edge of the 

 continental shelf. The depth of water between the 

 islaads and the mainland averages about 25 fathoms, 

 whde a few miles west the depth is some hundreds 

 of fathoms. The islands are composed entirely of 

 coral, all the rock above sea-level (the highest point in 

 any of the islands is 50 ft.) being uplifted coral rock 

 or sand. There are distinct traces of a very recent 

 uplift of about 8 ft., but at an earlier date — quite 

 recent geologically — a much greater uplift put the 

 islands in connection with the mainland. As a conse- 

 quence of this former land connection certain of the 

 islands are now inhabited by large numbers of walla- 

 bies, several species of amphibia, and many species 

 of reptiles. There is thus a combination of the 

 features of coral islands and the continental terres- 

 trial fauna. There is evidence that a warm tropical 

 current flows southwards and reaches the Abrolhos, 

 and possibly accounts for certain tropical characters 

 of the fauna of the islands. The neighbouring main- 

 land is bathed by cooler waters, probably of southern 

 origin. Prof. Dakin recorded from the islands a 

 considerable number of interesting animals, including 

 a new species of Ptyrhodera allied to P. flava. 



The Development of Trypanosomes in the Inverte- 

 brate Host. 



Prof. E. A. Minchin showed that if an analysis and 

 comparison be made of those instances in which it 

 can be claimed that the development of a given species 

 of trypanosome in its invertebrate host is known, it 

 is seen that in every such instance there is a part of 

 the developmental cycle which is constant in occur- 

 rence and uniform in character, and another part 

 which is of inconstant occurrence and variable in 

 character. 



* In the constant part of the cycle the parasite always 

 assumes the crithidial type of structure and multiplies 

 incessantly in this form to produce a lasting stock of 

 the parasite, certain individuals of which change 

 sporadically from the crithidial into the trypaniform 

 type and so become the final, propagative form of the 

 development, destined to pass back into the verte- 

 brate host and establish the infection in it. During 

 hunger-periods the crithidial forms may pass tem- 

 porarily, in some cases {e.g. the trypanosome of the 

 skate in the leech Pontobdella), into the resting, non- 

 flagellated leishmanial form, until food is again 

 abundant, when they form a new flagellum and revert 

 to the crithidial type of structure. 



The inconstant part of the cycle, when it occurs, 

 is intercalated at the very beginning of the develop- 

 ment in the invertebrate, and lasts but a relatively 

 short time ; it is derived directly from the trypano- 

 somes taken up by the invertebrate from the verte- 

 brate host, and takes the form of an active multipli- 

 cation of the parasites in either the trypaniform (e.g. 

 Trypanosoma gambiense in the tsetse-fly) or leish- 

 manial (e.g. T. cruzi in the bug Conorhinus) condi- 

 tion. In the cases where this early multiplicative 

 phase is wanting altogether, the trypanosomes taken 

 up by the invertebrate host pass at once into the 

 crithidial phase {e.g. T. vivax in tsetse-fly). 



When a further comparison is made between the 

 development of trypanosomes in the invertebrate host 

 and the development of the closely allied species of 



