648 



NATURE 



[October 22, 1908' 



number of species i? not large. The large quantities of 

 Entomostraca — principally copepods and Cladocera — doubt- 

 less form the food supply of the fishes, which occur in 

 astonishing abundance ; fifteen species of fish were 

 obtained, all of which are well-known Nile forms. The 

 swampy pools on the margin of the lake yielded ostracods, 

 hydrachnids, and spiders. The MoIIusca' obtained belong 

 to eleven species— two only of which are lamellibranchs— 

 all of which are Nilotic forms. Paranais littoralis, a 

 small oligochaete, was the only aquatic worm obtained, no 

 leeches or Turbcllaria being seen. Cordylophora was found 

 growmg in great abundance in the lake, an interesting 

 fact, as it has not previously been recorded from Africa. 

 Of especial interest are the presence in the lake of (i) a 

 gymnolaematous polyzoon with a circular lophophore and 

 eight _ tentacles, and (2) a medusa and the associated 

 hydroid stage — Mocrisia /vonsi— which appear to bear a 

 resemblance to Sarsia. Mr. Boulenger added further 

 details regarding Mrerisia, and discussed its importance in 

 relation to the possible former history of the lake. 



Structure of Dendrosoma radians. 



Prof. S. J. Hickson and Mr. J. T. Wadsworth conclude 

 that the bodies described by Kent as the " exogenously 

 produced germs " of Dendrosoma are epizoic, or possibly 

 parasitic, Acinetaria belonging to the genus Urnula. The 

 only true reproductive bodies of Dendrosoma are the so- 

 called internal buds or gemmulae, first described and figured 

 by Levick. The micronuclei of Dendrosoma are 4 ;u in 

 diameter when they have reached their full size ■ when 

 m division the length of the spindle is 24 /x, and the 

 chromosomes are numerous and minute. No centrosomes 

 were seen, nor has conjugation been observed. 



Haematozoa from Ceylon Reptiles. 



Miss Muriel Robertson described several Hjematozoa 

 from Ceylon reptiles. The multiplication of Haemo- 

 gregarina nicoriae takes place in tortoises (Nicoria and 

 Emyda), and the transmitting host is a species of 

 Branchellion, in the alimentary canal of which the ha>mo- 

 gregarine becomes motile. Trypanosoma vittatae and 

 Haemogregarina vittatae are found in Emyda vittata, and 

 the transmitting host of both is a species of Glossiphonia. 

 Other haemogregarines, trypanosomes, and a Htemo- 

 cystidium were described from lizards (,e.g. Hemidactylus). 

 (Other papers on trypanosomes and Piroplasma were 

 given before a joint meeting of Sections D and I ; for an 

 account of these see " Physiology at the British Associa- 

 tion, Nature, October 8, p. 593). 



Giant Nerve Cells and Fibres of Halla. 

 Dr. J. H. Ashworth described the structure and histology 

 of the giant nerve cells of the polychjete Halla partheno- 

 peia. These cells, of which there' are usually fifteen to 

 eighteen in each worm, are distinguished by ' their large 

 size (they may attain a diameter of 150 '^) and thick 

 sheath. Fine chromophilous granules are present in the 

 protoplasm (except in a peripheral zone, from which they 

 are almost or quite absent) in varying amount in different 

 giant cells. They are found in greatly increased mass in 

 a specialised perinuclear zone, the outer edge of which 

 is bounded by the perinuclear network of neurofibrillje, 

 which is thus in a position which facilitates its rapid 

 nutrition. In the general protoplasm of the cell there is 

 a network of neurofibrillse, generally wider meshed and 

 more slender stranded than the perinuclear network. 

 I-rom the intracellular network slender, primitive fibrils 

 pass towards the giant fibre, and several stouter fibrillfe— 

 si.K to ten from small cells, twelve to thirty from large 

 cells— each formed by the fusion of several primitive fibrils, 

 pass into the giant fibre, forming a bundle which occupies 

 from one- to three-fourths of the lumen of the fibre. The 

 fibrillae in the giant fibre are generally of the same thick- 

 ness, but occasionally one, two, or three fibrils are thicker 

 than the rest. The contents of the giant fibre are 

 equivalent and have a similar structure to the axis cylinder 

 of a medullated nerve fibre, except that in the former there 

 is nothing comparable to the nodes of Ranvier of the 

 latter. 



NO. 2034, VOL. 78] 



The ]'ascular System of Stylodrilus. 

 Mr. R. Southern directed attention to certain features 

 of the vascular system of a new species of Stylodrilus 

 from the River Annalee, co. Cavan. This differs from 

 all other species in the presence of simple contractile 

 saccular appendages on the posterior portion of the dorsal 

 vessel, a condition intermediate between that seen in 

 normal lumbriculids and that in the aberrant genus Stylo- 

 drilus. The relations of the dorsal and ventral vessels to 

 the intestinal blood sinus were also described, and shown 

 to differ considerably from those usually met with in 

 oligocha;tes. 



The Respiration of Land Isopods. 

 Mr. E. E. Unwin pointed out that woodlice are derived 

 from aquatic ancestors, and, having taken to terrestrial 

 life, have adapted their respiration to their altered environ- 

 ment. The different kinds of woodlice are, according to 

 the speaker's experiments, suited to different degrees of 

 dryness; e.g. Trichoniscus pusillus soon dies unless kept' 

 very damp, while Porcellio scaber can live four or five 

 days in a dry box. Ligia oceanica, Trichoniscus pusillus, 

 Oniscus aselhis, Porcellio scaber, and Armadillium vulgare 

 are arranged in order according to their habitat, and the 

 structure of their respiratory organs shows a corresponding 

 gradation from simple gills to gills supplemented by air 

 tubes ramifying through some of the abdominal exopodites. 



The Distribution of Irish Fresh-water Mites. 



Mr. J. N. Halbert contributed some notes on the dis- 

 tribution of Irish fresh-water mites (Hydrachnida), point- 

 ing out that they may be divided, like the fresh-water 

 mites in general, into two great faunistic groups : — (i) a 

 group containing those widely distributed species which 

 inhabit standing and slowly flowing waters of a com- 

 paratively high temperature, and (2) a group embracing 

 those forms which are found in waters of a constantly 

 lower temperature, especially those of cold highland lakes 

 and streams. 



Arctic and Antarctic Collcmbola. 



Prof. G. H. Carpenter pointed out the comparative 

 richness of the collembolan fauna of the remote northern 

 and southern lands. The Poduridae and Isotomins are 

 believed to be nearest to the primitive stock of the order, 

 while the Entomobryince, the Tomocerlnae, and the 

 Symphypleona are more highly specialised. It is sug- 

 gestive that in both Arctic and Antarctic faunas the 

 primitive genera are well represented, while the specialised 

 genera have very few species. Two Arctic isotomines are 

 present in our own islands — Agrenia bidenticulata, found 

 last year in Irish and Scottish mountain streams, and 

 Proisotoina bcschii, which inhabits the Arctic regions of 

 botK the Old and New Worlds and the coast of Scotland. 

 " Bipolarity " in the Collembola is shown by Wahlgren's 

 record of the latter species from Tierra del Fuego ; a 

 closely allied form is present in the South Orkneys. Such 

 distribution indicates a high antiquity (probably Mesozoic) 

 for this form. Several genera are apparently confined to 

 the southern regions ; for instance, Cryptopygus is repre- 

 sented by identical or nearly allied species in Tierra del 

 Fuego, Graham Land, South Shetland, South Orkneys, and 

 South Georgia, while Isotoma octo-oculata is present in 

 Graham Land, South Shetland, South Orkneys, and 

 Kerguelen, and the Isotoma of South Victoria Land is 

 closely allied to a Fuegian species. Such distributional 

 facts suggest the considerable geological age of the spring- 

 tails and a former wide extension of the .'\ntarctic con- 

 tinent. The National Antarctic (Discovery) Expedition 

 collected from moss at Granite Harbour, South Victoria 

 Land, a remarkable springtail, referable to the PoduridjE, 

 but showing some striking affinities to the Isotominje, 

 which is apparently the most southerly terrestrial animal 

 yet known. 



Mimicry in Lepidoptera. 



Dr. F. A. Di.xey pointed out that when Fritz Miiller 

 put forward, in 1879, his theory of common warning 

 colours, or the assimilation of one distasteful form to 

 another for the sake of mutual protection against 

 insectivorous enemies, he recognised the probability, or 



