December io, 1914] 



NATURE 



407 



Crithidia (e.£. C. melophagia in the sheep-ked) and 

 Leptomonas, which have no alternation of hosts or 

 generations, but are confined during their entire life- 

 history to particular species of invertebrate hosts, it 

 is seen at once that the life-cycles of these parasites 

 of invertebrates are similar in all essential points to 

 the crithidial phases of trypanosomes in their inverte- 

 brate hosts. It is evident, therefore, that the crithidial 

 phase in the development of a tr\panosome is to be 

 interpreted as a reversion to, or recapitulation of, the 

 type of development that occurred in the ancestral 

 form which was originally a parasite of the inverte- 

 brate alone, before it had obtained a footing in the 

 vertebrate host or had acquired the trypanosome-like 

 type of structure ; while the multiplicative phases of 

 variable character preceding the crithidial phase in 

 tr3-panosome-development are to be regarded as having 

 been intercalated secondarily into the life-cycle and of 

 no phylogenetic significance. 



Australian Haematozoa. 



Dr. J. Burton Cleland remarked that, owing to the 

 geographical isolation of Australia, the study of the 

 blood-parasites of the vertebrates, especially of such 

 as have no easy means of passing over stretches of 

 ocean, is of considerable interest. In some cases, 

 e.g. the marsupials, speculation arises as to whether 

 the haemogregarines found in them reached Australia 

 (i) with the marsupials when these originally came; 

 (2) as parasites of the invertebrate host by a separate 

 arrival ; or (3) whether their appearance represented 

 the adaptation in Australia of a parasite, at one time 

 confined to an invertebrate host, to a habitat partly 

 in a vertebrate and partly in an invertebrate host. 

 Dr. Cleland considered the first of these suggestions 

 to be the most reasonable. He directed attention to 

 the records of the principal protozoon parasites of 

 the blood of Australian vertebrates. Plasmodium 

 seems to be rare in birds, while Halteridium is com- 

 mon. Trypanosomes have been found in several 

 species of birds, and often in the same infected birds 

 are large parasites, apparently the intracorpuscular 

 form of the trj-panosome. 



Australian Trematodes and Cestodes. 

 Dr. S. J. Johnston passed in review the principal 

 Australian Trematodes and Cestodes, and stated that 

 the entozoan fauna of the host-animals belonging to 

 any particular class of vertebrate might be separated 

 into two divisions : (i) those which have been para- 

 sitic in these hosts for a very long time, practically 

 from the first appearance of the host-animals ; and 

 (2) those which represent more recent acquirements. 

 The members of the former division may be readily 

 recognised by the fact that they have near relatives 

 parasitic in other branches of the same stock, while 

 members of the latter division generally have not. 

 The members of each genus (or sometimes of several 

 closely related genera) in the former division, in many 

 cases scattered all over the world, constitute a natural 

 group, and must be regarded as derived from common 

 ancestors. These ancestors were parasites of the pro- 

 genitors of the host-animals in the verv early days 

 when the group was much more restricted in its dis- 

 tribution than it is at the present time. A study of 

 the relationships and distribution of the parasites 

 affords some circumstantial evidence of the past move- 

 ments and paths of dispersal of the host-animals. 

 Dr. Johnston instanced the entozoan fauna of marsu- 

 pials in Australia, which comprises a number of 

 Cestodes (e.g. Linstowia) and Trematodes (e.g. 

 Harmostomum), the nearest relatives of which are 

 found in species of the same genera which live para- 

 sitic in South American marsupials. 



NO. 2354, VOL. 94] 



Parasitic Worms of Queensland. 



Dr. \\"m. Nicoll stated that the hook-worms, 

 Ankylostoma and Necator, are the most commoti 

 human parasites in Queensland, but these worms are 

 not more common there than in temperate regions. 

 Hydatids are much rarer in Queensland than in other 

 parts of Australia. Dr. Nicoll gave a brief general 

 account of the more important parasites observed in 

 animals in Queensland, and referred in particular to 

 Onchocerca gibsoni, the round-worm which causes 

 nodular disease in cattle. The life-histor)- of this 

 worm still remains unknown, but a considerable 

 amount of experimental work has been carried out 

 thereon. It has been suggested that infection is 

 either direct (taking place in young animals) or b\- the 

 agency of some biting insect. Dr. Breinl's experi- 

 ments indicate the possibility of infection by means 

 of water, for he was able to induce larvae of Oncho- 

 cerca to pass out through the unbroken skin, and tc 

 emerge into water where, however, they lived only 

 a short time. Attempts to infect various aquatic 

 animals with the larvae were unsuccessful. Larvae 

 ingested by the stable-fly (Stomoxys) were able to live 

 therein for several days, but Dr. Cleland could not 

 detect any development in these larvae. Dr. Nicoll 

 applied sterile water on a calico pad, or in a glass 

 vessel, to the skin of a cow over an Onchocerca 

 nodule, but did not obtain larvae. Experiments on 

 excised nodules placed in water showed that the larvae 

 can, and do, make their escape through the capsule 

 enveloping the worm-nodule, and therefore may be 

 found close to the surface of the body in such posi- 

 tions that they can be readily ingested by a biting 

 insect. 



Studies on Echinodertn Larvae. 



Dr. T. Mortensen gave an account of his recent 

 work at Misaki (Japan), undertaken with the object 

 of studying the inter-relationships between larval and 

 adult forms of Echinoderms, and of testing the view 

 that within the different families the larvae have cer- 

 tain structural features in common, for if this prove 

 to be a general rule larval characters may be of con- 

 siderable importance in helping to settle doubtful 

 cases in Echinoderm classification. Dr. Mortensen 

 reared more or less completely sixteen Sf)ecies. Among 

 these were three Temnopleurids, the larvae of which 

 have been hitherto unknown. This family has a 

 special form of larva characterised by peculiarities of 

 its skeleton. Four species of Clypeastroids — Ch- 

 Peaster japonicus, Mellita sp., Laganum fudsiyama. 

 and L. decagonale — were reared ; their larvae all proved 

 to be of the type characteristic of other Clypeastroids. 

 L. fudsiyama is a deep-water species (200-1000 

 metres), and this is the first time that the larva of 

 a deep-water Echinoderm has been reared. The larva 

 is pelagic and of typical Clypeastroid structure. 

 L. decagonale has large eggs, rich in volk. and in 

 correlation with this the development is shortened, 

 the whole metamorphosis being completed in three 

 to four days. The lar\-a takes no food, the mouth 

 being rudimentary; there is no ciliated band, but a 

 strong general cil'iation. The larval skeleton is rudi- 

 mentary, but of the usual Clypeastroid form ; onlv 

 four larval processes at most are developed, but 

 generally only two, sometimes one, three, or none. 

 Asterina pectinifera was found to have a pelagic larva, 

 while the two other species, the development of 

 which is known, take care of the brood and have 

 non-pelagic larvae. The larva of this species has a 

 Brachiolaria stage, thus proving the correctness of 

 the view that the lar\'al appendages in the voung 

 A. gibbosa are homologous with the brachiolarian 

 processes of free-swimming lar\-as. 



