120 



KNOWLEDGE. 



April, 1915. 



HYBRID COCKATOOS— Dr. Ernest Warren, of the 



Natal Museum, describes a very interesting case oi hybridism. 



The male bird was the common Sulphur-crested Cockatoo 



itua galsrita), the female the so-called Slender-billed 



Ltoo {Licmetis nasiea). The hybrid seemed to be a 



thorough Mind. Out of ten characters it was nearer 



Cacatua in five, nearer Licmetis in one. and almost exactly 



intermediate in four. In even,' character examined, with 



the possible exception of the coloured and non-coloured 



lores, there is very obvious blending of the male and female 



tics. There was no evidence of Mcndelian 



inheritance. 



HABITS OF TESTACELLA.— The Testacellid Slugs 

 widely from the other British Slugs: Limacidae and 

 Aiionidae. They retain a small external shell, visible on 

 the surface, near the posterior end, whereas in the others 

 the shell is either a hidden vestige or quite absent. Again, 

 while most British Slugs are omnivorous, the Testacellids 

 are essentially carnivorous, and feed largely on Earthworms 

 caught by night. Mr. Charles Oldham writes : " The 

 Earthworm is seized by a sudden, rapid extrusion of the 

 Slug's odontophore or lingual ribbon, a structure provided 

 with close-set rows of long, slender, barbed teeth, which 

 afford an excellent hold on the Worm's soft body, and the 

 whole of this stupendous meal, in bulk perhaps three times 

 that of the Slug, is gradually ingested." In its early 

 struggles the Earthworm often dashes the Slug about, 

 but the bull-dog grip is not relaxed. In hot, dry weather 

 and in the cold of winter Testacella lies inactive in a cocoon- 

 like cell made of earth and mucus. The elliptical eggs, 

 about five millimetres in longer axis, are deposited under- 

 ground. There are three British species. 



STRENGTH OF SPONGE-CURRENTS.— Ever since 

 Robert Grant discovered the currents produced in water 

 by living sponges the hidden activity of these often very 

 vegetable-like animals has excited interest. The last con- 

 tribution to the subject is Professor G. H. Parker's estimate 

 of the strength and volume of the currents. In Stylotella 

 the pressure is equal to a column of water 3-5-4 millimetres 

 in height. In seven others it was less, usually a little over 

 two millimetres. In Spitwsella sororia, the common Ber- 

 muda finger-sponge, a tube put into an exhalent aperture, 

 or osculum, showed that the rate of flow is about four 

 millimetres per second, and the rate of discharge about 

 seventy-eight litres per day from each osculum — over 

 four hundred and fifteen gallons for the whole sponge. 

 As the experiments were made in the laboratory, the esti- 

 mate is probably under the mark. An undisturbed specimen 

 of Spirastrella at low water was found capable of over- 

 coming a pressure of four millimetres of sea water. Big 

 sponges often produce deformations of the surface of the 



sea above them, as a vigorous spring does ; but Professor 

 Parker's interesting investigations indicate that the cur- 

 rents flow at low pressure. 



COMPANIONS OF J 1 l.l.YFISHES.— It is well known 

 that some medusae swim about with horse-mackerels 

 (Carangidae) in the shelter of their Sowing lips. Mr. S. F. 

 Light describes this in a Philippine jellyfish, Rhopilema 

 visayana, with which a species of Caranx has established a 

 companionship. " The fish would be seen playing about 

 among the mouth, arms, and appendages, and on being 

 alarmed would disappear under the edge of the bell, 

 between the arms or in the subgenital porticus." A similar 

 condition was found in the case of Lobonema mayeri. Inside 

 the Rhopilema there was usually a crab (Char ibdis crucij era) , 

 considerably paler than is typical for the species, which 

 suggests a prolonged residence within the medusa. It is 

 interesting to notice Light's observation that the companion 

 fishes were seen eating dead specimens of Rhopilema visayana, 

 though their relation with the living forms seemed to be 

 quite friendly. " I am told," Mr. Light adds, " that 

 R. visayana, which is closely related to the common edible 

 medusa of Japan (R. esculenta), is used for food by the 

 inhabitants of the east coast of Leyte, where it is preserved 

 in vinegar." 



COLOUR CHANGE OF NEWTS.— The colour changes 

 of the Palmated Newt (Molge palmata) are well described by 

 Mr. Charles Oldham. " Individuals living in a pond with 

 a dark, muddy bottom are dark green in colour, and in 

 consequence when at rest are almost invisible from above ; 

 similarly those in a pond with a bottom of yellow clay 

 are yellowish in colour and alike inconspicuous. If, how- 

 ever, one of the dark green Newts be placed in a glass 

 vessel upon a white surface, it will, in the course of a few 

 hours, become yellowish-drab in colour, but often paler in 

 tint than the Newts which rested on the yellow clay; 

 whilst, if one of the yellow-skinned Newts be taken from 

 the pond with the bottom of yellow clay and placed into a 

 glass vessel, it will be seen presently to exhibit greenish 

 spots and marblings over the whole of the upper surface, 

 and ultimately, by the expansion of these green areas, to 

 acquire an almost uniform dark-green tint over the whole 

 of the surface exposed to view from above. The green 

 will, indeed, be darker in tint, provided the glass vessel 

 stands upon some dead-black surface, than in the Newt 

 which was taken from the pond with the bed of dark mud." 

 (Trans. Hertfordshire Nat. Hist. Soc, Volume XV, 1915, 

 page 207.) The colour-change depends on the contraction 

 and expansion of the living matter of the pigment cells, 

 which are under the control of peripheral nerves. The 

 stimulus from the coloured environment first affects the 

 eye, for blind animals do not change. 



NUMBER OF SPORES IN A MYXOMYCETE. 

 By W. B. GROVE, M.A. 



In November, following the directions of Mr. S. P. Bolton, 

 I found on a tree-stump a huge mass ot aethalia of the 

 Myxomycete (Brefeldia maxima). The crowded aethalia 

 covered a space of about six square feet, and were just 

 ripening their spores. As the number of spores was evi- 

 dently enormous, it was thought it would be interesting to 

 make an estimate. For this purpose a gramme of spores 

 and capillitium was taken and shaken up in two hundred 

 cubic centimetres of water, with a little ether to loosen the 

 spores from one another. After thorough shaking, the number 

 of spores was counted, in the ordinary way, by a blood- 

 corpuscle-counting apparatus of Zeiss. Allowing about 

 six per cent, for capillitium, the number worked out at 

 10 s in a cubic centimetre. Thus, in the whole mass 

 covering the stump, roughly estimated at about five hundred 



cubic centimetres, there were half a million million spores. 



This result can be checked by geometrical considerations. 

 The aethalium contains nothing but spores and capillitium ; 

 the size of the spores varies from 9 to 12^. Taking 10/i 

 as an average, the volume of a spherical spore is 

 approximately \ • (j^) 6 cubic millimetres. 



If equal spheres are packed as tightly as possible in a 

 given space, geometry teaches us that about twenty-six per 

 cent, must be allowed for the spaces between the spheres ; 

 if, then, we allow six per cent., as before, for capillitium, 

 and a further eighteen per cent, for the obvious loose packing 

 and occasional larger spores (this last amount is, of course, 

 a mere guess), we get a total allowance of fifty per cent. 



Therefore the number of spores in one cubic centimetre 

 = 50% of 2xl0°xl0 s = 10 9 . 



