igo 



NA TURE 



[JUNE 20, I 90 1 



photometer ; and they have readily adapted themselves to the 

 somewhat special manipulation and observation which it requires 



The phenomenon of "accidental double refraction," which 

 occurs in liquids when these are subject to changes of shape, or, 

 to describe more correctly, rates of strain, forms the subject of 

 an article by Prof. Ladislaus Natanson in the Btilletiu of the 

 Cracow Academy. The author gives an investigation, mainly 

 hydrodynamical, of the case where the rates of strain are pro- 

 duced in a viscous liquid contained in the space between a rotating 

 cylinder and a concentric cylindrical envelope. A formula is 

 found connecting the angular velocity of the cylinder with the 

 double refraction per unit length, and this formula appears to 

 agree well with some of the e.vperimental results of Umlauf and 

 De Metz. 



An illustrated article on the Kress flying machine appears in 

 Die Utnschau for June 8. As has been stated in previous 

 accounts in several journals, the apparatus is a multiple winged 

 machine attached to a light boat, and the proposed method of 

 experimenting is to drive the boat through the water until a 

 sufficient speed has been attained for the thrust on the wings to 

 cause it to rise from the surface. The writer of the article, 

 however, evidently considers that the construction of the "air 

 ship"has been somewhat prematurely pushed forward, seeing that 

 the most important part of the apparatus, namely, the motor, is not 

 yet ready. He also is of opinion that the problem of landing has 

 not been sufficiently studied. Several experiments have already 

 been made with the apparatus, without, however, leaving the 

 water ; but it will be when the machine has been made capable 

 of lifting itself into mid-air that the chief difficulties of the 

 investigation will arise. 



The fourth annual dinner of old students of the Centra] 

 Technical College will be held on Wednesday, July 3, with 

 Prof. O. Henrici, F.R.S., in the chair. Tickets can be obtained 

 from the honorary secretary, Mr. Maurice Solomon, 12 Edith 

 Road, West Kensington. 



Capt-j^in Stanley Flower sends us his Report, as director, 

 of the Ghizeh Zoological Gardens for the year 1900. The list 

 of donations is a satisfactory one, and we are glad to note that 

 very much has been effected during the year in the way of adding 

 new buildings and improving old ones, as well as in making 

 additional aviaries and enclosures in the gardens. 



In the first part of a new biological journal — the Bulletin of 

 the Brooklyn Institute — Mr. A. G. Mayer discusses the 

 variations displayed by a species of Medusa from the Florida 

 seas. The species in question is considered to have been 

 derived very recently from a form common in Florida waters, 

 but to be so distinct as to constitute a genus by itself. " It 

 is remarkably variable, and its great commonness attests to its 

 successfulness in the struggle for existence. In its variations it 

 illustrates the manner in which other newly arisen races of 

 animals may have suddenly given rise to still more diverse 

 species." 



Parts ii. and iii. of the third volume of Annolationes 

 Zoologicae Japonenses are devoted to a list of the fishes of Japan, 

 by Messrs. Jordan and Snyder. A total of 6S6 species are 

 recognised. Apart from its importance to the students of 

 ichthyology, this communication is worthy of the best attention 

 of those interested in the distribution of marine animals, as the 

 authors have been enabled to divide the Japanese marine fish- 

 fauna into four distinct groups. There are the northern or 

 Yezo group, the temperate or Nippon group, the semitropical 

 or Kiusiu group, and the Bassalian or deep sea group. The 

 fish fauna of the Kurile Islands, which is probably very similar 

 to that of Kamchatka, belongs to a distinct subarctic group, 

 while that of Formosa probably pertains to the tropical Malayan 

 assemblage. 



NO. 165 I, VOL. 64I 



The structure of the hairs of the Patagonian ground-sloth 

 and of the living South American edentates forms the subject 

 of an essay by Dr. W. G. Ridewood, which appears in the May 

 issue of the Quarterly Journal of Microicopical Science. The 

 most generally interesting of the author's observations are those 

 relating to the hairs of the two living types of sloth, and the 

 structure which permits of the growth of an alga in each. In 

 the three-toed sloth the hair is invested with a thick extra- 

 cortical layer. "The layer has a tendency to crack in a trans- 

 verse direction, and in the cracks there come to lodge unicellular 

 alga;, to which Kuhn has given the name Plettrococcus bradypi. 

 The moisture of the climate in which Bradypus lives enables the 

 alga to live and propagate in this curious position, and the sloth 

 acquires a general green tint which must render it very diflicult 

 to distinguish as it hangs among the green foliage." In the 

 two-toed sloth, on the other hand, the bulk of the hair is com- 

 posed of cortex which is longitudinally fluted or grooved, the 

 grooves being filled with strands of extra-cortex in which 

 flourishes an alga {Pleiirococcus choloepi) distinct from the one 

 infesting the hairs of the three-toed species. Of quite a different 

 type are the hairs of the ground-sloth, which are smooth and 

 solid, Dr. Ridewood rejecting the idea of Dr. Lonnberg that 

 they were originally coated with a cortex that has now perished. 

 An important biological contribution to the same journal is 

 the life-history of a North American bivalve mollusc, Nuciila 

 delphinodonta, by Prof. G. A. Drew, of the University of 

 Maine. 



Under the title of "Zoological Gleanings from the Royal 

 Indian Marine Survey Ship Investigator" Major .\lcock has 

 collected together the biological observations made by the 

 different medical officers who have served on board during 

 his own connection with the vessel. These observations, the 

 author tells us, are buried in reports that are not readily ac- 

 cessible, or scattered through papers on systematic zoology 

 where they may easily be overlooked. The observations are 

 arranged under eight headings, namely, commensalism ; sexual 

 characters, pairing and viviparity ; sounds made by marine 

 animals ; notes on stalk-eyed crustaceans ; instances of pro- 

 tective and warning coloration ; phosphorescence ; peculiarities 

 in food of marine animals ; and notes on reptiles and fishes. The 

 ''gleanings" are really a mine of information to the naturalist, 

 and the author has rendered a distinct service to his fellow- 

 workers in producing them in their present form. Among 

 notable instances of commensalism is the case of the hermit- 

 crab protected by a bag of sea-anemones. Another instance 

 has often been observed on the reefs of the Andamans, where a 

 crab of the genus Cryptodromia is protected by a sponge, which 

 is shaped like a cap and tightly fitted to the crustacean. 



Geological students and others interested in the science 

 of the earth will find many desirable works in a classified cata- 

 logue of books and pamphlets on geology just issued by Messrs. 

 Wesley and Son. The catalogue contains no less than 2225 

 titles of works in various departments of geological science, 

 cla.ssified under 28 headings. It includes the geological library 

 of the late Mr. G. H. Morton, of Liverpool. A glance through 

 the catalogue will repay any geologist anxious to increase 

 his library. 



The cryptogams collected by Dr. F. Welwitsch in 1853-1S61 

 are described by the botanists who have determined them in the 

 new volume (vol. ii. part ii.) of the "Catalogue of Welwitsch's 

 African Plants," published by the trustees of the British 

 Museum. Though the plants were collected more than forty 

 years ago, the collection is in some respects the most extensive 

 and representative yet obtained from Africa. The species now 

 described belong to the vascular cryptogams, mosses, hepatics, 

 marine algce, freshwater alga;, diatomacese, lichenes, fungi and 

 mycetozoa. 



