552 



NA rURE 



[September 27, 1906 



strain on the lesources of the Dogger Bank. Dr. Master- 

 man and others advocated the attacking of special problems, 

 and thought that the more general questions might be for 

 the present postponed. 



Systematic Study of Oicanic Plankton. 

 Dr. G. H. Fowler put forward some suggestions for the 

 more systematic study of oceanic plankton. Evidence that 

 temperature appears to be the chief determinant in the dis- 

 tribution of plankton was cited, the highest depth of a 

 species being the position of its maximum, the lowest 

 depth that of its minimum, temperature at any given 

 geographical position. It was urged that, for the solution 

 of the problems demanding attention, oceanic expeditions 

 should be confined to the systematic study of small areas 

 instead of making long voyages, that the upper zones of 

 water should be more carefully investigated than has 

 hitherto been the case, and that standard tow-nets should 

 be adopted internationally by all expeditions in order to 

 afford means of comparison of the fauna in different seas 

 and under different conditions. 



Life Cycle of the Protozoa. 



Prof. Calkins referred to some features in the life cycle of 

 the Protozoa, and urged that the whole life cycle should 

 be worked out before a new species could be regarded as 

 safely established. This safeguard would prevent confusion 

 and the undue multiplication of species. Prof. Calkins 

 showed, for example, that two such well-known and appar- 

 imtly fixed species as Paramoccium caudatum and aurelia 

 are no longer to be regarded as distinct. During the progress 

 of a culture of P. caudatum, an individual appeared with all 

 the characters of P. aurelia (including form of body and 

 double micronuclei), but after forty-five generations, the 

 organisms being watched daily, the aurelia characters were 

 lost, and the entire race became P. caudatum again. In 

 any such life cycle the organisms pass through phases of 

 vitality comparable to the different age-periods of Metazoa. 

 There are periods of (i) youth, characterised by great vigour 

 of cell multiplication; (2) maturity, indicated by changes in 

 the chemical and physical balance of the cell, accompanied 

 by differences in size or protoplasmic structure, leading to 

 the formation of conjugating individuals, with or without 

 sexual differentiation ; (3) in forms which do not conjugate, 

 old age or senescence, ending in death. In many forms, 

 especially where dimorphic gametes are produced, the 

 period of sexual maturity leads directly to that of old age, 

 and gametes which fail to conjugate soon die without 

 further multiplication, as in the majority of Sporozoa and 

 in many Rhizopods. In Ciliata, although failure to con- 

 jugate is finally fatal, many generations may be formed 

 before death occurs, and in these may be studied the 

 peculiar cytoplasmic changes which accompany protoplasmic 

 senility. While working at the maturation phenomena in 

 Paramcecium, Prof. Calkins and Miss Cull were able 

 to show that the curious crescent form assumed by the 

 micronucleus is the stage of synapsis, the chromosomes 

 being double at this time, apparently by union side by side 

 in typical parasynapsis. The two following maturation 

 divisions have not yet, however, been completely followed. 

 The speaker also dealt with the subjects of fertilisation 

 and parthenogenesis, pointing out that the latter has only 

 a limited success, acting merely to postpone or counteract 

 physiological death (Hertwig). Physiological and germinal 

 death in" Protozoa are connected with exhaustion of vitality 

 and of definite substances in the cell. 



Infection of Monkeys with Guinea-worm. 



Dr. R. T. Leiper described some results obtained by the 

 infection of monkeys with guinea-worm. These confirm 

 the view that Filaria medinensis gains access to the human 

 host bv introduction in the larval stage (while still con- 

 tained ' within its intermediate host, Cyclops) into the 

 stomach in drinking water. The larvae are released and 

 stimulated into activity by the gastric juice. .\ monkey 

 which had been infected 'in this way was killed after six 

 months, and five guinea-worms — three unfertilised females 

 and two males (each of the latter 22 mm. long)— were 

 found. No experimental evidence could be obtained in sup- 

 port of the theory which has, during recent years, been 



N". 1926, VOL. 74] 



favourably received in this country, that the causal agen« 

 in the disease invades the body through the skin, nor was 

 a repetition of Plehn's experiment of feeding monkeys with 

 freshly discharged embryos attended with the slightest 

 success. 



Habits of Tube-huilding Worms. 

 Mr. Arnold T. Watson gave an account of the habits of 

 tube-building worms. He showed how Sabella collects, 

 by means of its branchial tentacles, particles which are 

 applied by means of the collar lobes to the outside of a 

 mucous tube secreted by the epidermis. As a safeguard 

 against the intrusion of an enemy, the mouth of the tube 

 usually collapses when the worm retracts, but in one of 

 the rock-boring species the end of the tube rolls up like 

 the frond of a fern. Terebella builds its tubes of sand, 

 shells, or gravel, terminated by an arborescent arrange- 

 ment composed of single grains of sand or other suitable 

 material. Pectinaria produces the well-known conical 

 sand-tubes, the material for which is selected with great 

 care. Owenia constructs a flexible tube by attaching in 

 an imbricating manner flat sand grains and fragments of 

 shell to a membranous tube secreted by special epidermal 

 glands. Panthalis weaves a massive tube composed of 

 threads supplied by the parapodial glands. These tubes 

 are open at both ends, but the worm is defended from 

 attack by a series of internal valves at each end of the 

 tube, which are automatically closed by the inrush of sea 

 water immediately the inmate of the tube retracts itself. 



Papers on Lepidoptera. 



Prof. E. B. Poulton exhibited a series of forms of Acraea 

 johnstoni, Godm., showing that each one of the protean 

 series of varieties has been evolved in relation to a Danaine 

 or Acraeine model, the models and mimics occurring 

 together on the slopes of Kilimanjaro. 



Dr. F. A. Dixey exhibited butterflies, some possessing 

 an epigamic scent, others an aposematic or warning scent, 

 and others in which both kinds of scent existed inde- 

 pendently. It is well known that the male of Ganoris 

 napi, one of our common white butterflies, exhales a frag- 

 rant scent (compared to that of lemon verbena) which is 

 probably epigamic in significance. Dr. Dixey has found 

 similar, though weaker, scents in the males of other British 

 Pierina;, Satyrinse, and Lycsenidae, and many of the native 

 African species were also found to possess an agreeable 

 odour suggestive of chocolate, vanilla, or the scents of 

 various flowers. These scents are generally distributed by 

 specialised scales (androconia), the distribution being, to 

 some extent, under control, the perfume being economised 

 when not needed in courtship. The offensive odours are 

 more or less shared by both sexes, but are sometimes 

 stronger in the female, and generally occur in forms which, 

 on independent grounds, are believed to be protected. 

 These aposematic odours are usually perceptible even in 

 uninjured specimens, but are much more evident when the 

 thorax is crushed. 



Mr. G. T. Porritt read a paper, full of details, on 

 melanism in Lepidoptera. He pointed out that melanism 

 had increased with extraordinary rapidity in south-west 

 Yorkshire and parts of Lancashire, and also occurred, to 

 a less extent, in other parts of the United Kingdom. In 

 some cases (e.g. Amphidasys hcliilaria, Odontoptera 

 hidentata) the change has been sudden, but in most cases 

 there has been a gradual, though rapid, change from pale 

 to black. More than thirty species are melanic in York- 

 shire, most of which have become so during recent years, 

 and there are other species which are tending in the same 

 direction. Many of these melanic forms will probably, at 

 no distant date,' oust the ordinary pale forms. The variety 

 varleyata of .Abraxas grossulariata has, however, not in- 

 creased, and, though known more than forty years ago, is 

 as rare now as it was then, although melanism is so 

 strongly impressed on the race that a brood reared this 

 year, from a pair of molhs from wild larva?, were all of 

 the exireme dark form, no single example showing any 

 tendency towards the pale ordinary form. The reasons for 

 and causes of the phenomenon were then discussed. The 

 usually accepted theory is that the darker colour renders 

 the insects less conspicuous as they rest upon the darkened 

 (by soot, moisture. &-c.) tree trunks, and, therefore, morr- 



