Oct. 21, 1880] 



NATURE 



595 



species make to live in are to a great extent formed of pellets of 

 their excreta. In 1874 he watched carefully the process of con- 

 structing the tubes in several species of Amphipoda. Microdcu- 

 topus grandimanus {^1/. minax. Smith) was a particularly 

 favourable subject for observation. When captured and placed 

 in a small zoophyte trough with srall branching algx, the indi- 

 viduals almost always proceeded at once to construct a tube, and 

 could very readily be observed under the microscope. A few 

 slender branches of the alga were pulled toward each other by 

 means of the antenna and gnathopods, and fastened by threads 

 of cement spun from branch to branch by the first and second 

 pairs of pera;opods. The branches were not usually at once 

 brought near enough together to serve as the framework of the 

 tube, but were gradually brought together by pulling them in 

 and fastening them a little at a time, until they \\ ere brought intp 

 the proper position, where they were firmly held by means of a 

 thick network of fine threads of ^cement spun from branch to 

 branch. After the tube had assumed very nearly its completed 

 form, it was still usually nothing but a transparent network of 

 cement threads woven among the branches of the alga, though 

 occasionally a branch of the alga was bitten oft" and added to the 

 framework : but very soon the animal began to work bits of ex- 

 crement and bits of alga into the net. In this case the pellets of 

 excrement, as passed, were taken in the gnathopods and maxilli- 

 peds, and apparently also by the maxilla; and mandibles, and 

 broken into minute fragments and worked through the web, upon 

 the outside of which they seemed to adhere, partially by the vis- 

 cosity of the cement threads, and partially by the tangle of 

 threads over them. Excrement and bits of alga were thus 

 worked into the v.'all of the tube until the whole animal was 

 protected from view, while, during the whole process, the 

 spinning of cement over the inside of the tube was kept up. 

 When spinning the cement threads within the tube the animal 

 was held in place on the ventral side by the second pair of 

 ■ gnathopod.-; and the caudal appendages, the latter being curved 

 beneath the anterior portion of the pleon, and on the dorsal side 

 by the third, fourth, and fifth pairs of pera^opods extended and 

 turned up over the back, with the dactyli turned outward into 

 the web. The spinning \\'as done wholly with the first and 

 second pera;opods, the tips of which were touched from point to 

 point over the inside of the skeleton tube in a way that recalled 

 strongly the movements of the hands in playing upon a piano. 

 The cement adhered at once at the points touched and spun out 

 between them in uniform delicate threads. The threads seemed 

 to harden very quickly nfter they were span, and did not seem 

 even from the first to adhere to the animal itself. 



Death bv H.\nging. — Recent experiments regarding the 

 nature of death by hanging or strangulation induce Prof. Tam- 

 masia to reject tlie view that the chief cause of such death is 

 compression of the pneumoga trie, causing paralysis of the heart 

 (Reale 1st. Loiitb., fasc. xiii.). In the great majority of cases, 

 he says, the proximate cause of death is the occlusion of the 

 respiratory passages. The greater or lesser rapidity of the death 

 depends on the degree of such occlusion. Compression of the 

 pneimiogastric and of the vessels of the neck may strengthen the 

 efficacy of that direct cause, but, in the absence of the latter, it 

 is insufficient to cause any instantaneous lethal phenomenon, as 

 some have supposed. 



H.«M0GLOiiiN IN ECHINODERMS. — The presence of haemo- 

 globin in the aquiferous system of an Echinoderm (O/ikiactis 

 urens, one of the Ophiurida) has lately been demonstrated by M. 

 Foottinger (Belgian Acad. Bull., No. 5). The only branches of 

 the metazoa in which it had not before been found were echino- 

 derms and zoophytes. Simroth observed certain globules in the 

 ambulacra! canals of the former, but not observing live indi- 

 viduals, he missed the hxmoglobin, which may be observed if one 

 of the arms of the living animal be broken ; a drop of red 

 colour appearing presently at the extremity. With the spectro- 

 scope the identity of the colouring matter with that of the blood 

 of vertebrates can be easily proved. The haemoglobin is con- 

 nected with globules, of varying form and size. Most have a 

 nucleus and are true cells. Along with these are free nuclei and 

 small unnucleated cor|juscles charged wilh haemoglobin. 



An Optical Property of the Cornea.— Prof. Fleischl of 

 Vienna has recently examined fresh corneas in polarised light, 

 and found that the corneal fibres became, under tension, doubly 

 refractive, and then occasionally give plienomena similar to those 

 occurring in starch granules (the theory of which has been 

 examined by von Lang). With this condition also is connected 

 the opacity of the cornea on rise of intraocular pressure. 



Phosphoric Acid in the Urine of Cows. — It is generally 

 supposed that the urine of herbivora does not contain phosphoric 

 acid. M. Chevron, however, lately had occasion (j5i;//. oV /M^aa'. 

 Roy. lie Belg., No. 8) to observe phosphates (a combination of 

 potassico-magnesian phosphate with bimagnesic phosphate) in 

 the urine of cows which had been receiving linseed oil-cake (iJ 

 kil. per .head daily), bran (ij kil.), beet -(25 kil.), and straw 

 (7iki!.), a diet which is rich in phosphoric acid (oil-cake and bran) 

 and in potash (beet). The phosphoric acid diminished and disap- 

 peared when green clover or lucern was substituted for the beet. 

 It appears from experiments made by Herr Bertram in Leipzig, 

 in 1S78, that lime has the property of eliminating phosphoric 

 acid from the urine of herbivora, and [M. Chevron points out 

 that the green fodder specified undoubtedly imparted more lime 

 than the beet did. He proposes further experiment, however, 

 to determine exactly the cause of elimination of the acid. 



Rudimentary Coma in Godetia. — While investigating the 

 development of the embryo sac in the different genera of Ona- 

 grace.-e, writes Mr. John M. Coulter, editor of the Botanical 

 Gazitt;, Indiana (vol. v. Nos. 8 and 9, p. 75), my attention was 

 attracted to certain hair-like projections which appeared upon 

 the forming ovule of Godetia (probably G. grandiflora). A care- 

 ful examination showed them to be identical in structure with 

 the forming hairs in the coma of Epilobium. They occurred 

 almjst exclusively at the chalazal end, one or t«o scattered ones 

 being detected farther down upon the raphe. A study of the 

 development of the coma of Epilobium shows that the first indi- 

 cation of it is a tuberculated appearance of the chalazal end. 

 Presently these tubercles push out into elongating nucleated cells, 

 which eventually develop into the long hairs of the coma. Now 

 Godetia permanently retains this tuberculated margin at the 

 upper end, but does not usually develop its coma any further. 

 In the cases examined, however, the forming ovules (either in 

 reminiscence or prophecy) stretched out their tubercles into 

 incipient hairs. Tracing these ovules in their subsequent deve- 

 lopment, it was found that these hairs gradually disappeared 

 until, when the ovules had become anatropous, there was no 

 indication of them. As Godetia has been merged iutolEnothera, 

 many species of the latter were examined, to see if any such 

 thing occurred in them ; but no trace of such growth was detected. 

 This would seem to indicate that if Godetia be not entitled to 

 generic rank, it is at least that part of CEnothera which ap- 

 proaches Epilobium. A discrepancy must, however, be noticed 

 here. In Epilobium the hairs of the coma do not begin to form 

 until the o\'ule has become completely anatropous ; but in 'the 

 Godetia observed the incipient coma had all disappeared by the 

 time the ovule had become anatropous, beginning to form before 

 the nucleus is half co /ered by the coats. These hairs appeared 

 in Greatest size and abundance when the axis of the ovule was at 

 right angles to its anatropous position. 



PHYSICAL NOTES 

 A beautiful illustration of the laws of polarisation of light 

 has lately been made by M. G. Govi. To understand it requires 

 a somewhat careful explanation. Let a parallel beam of light 

 be passed through a polariser, then through a thin slice of quartz 

 cut perpendicularly to the optic axis, then through an analysing 

 Nicol prism. It is seen, as is well known, to be coloured. This 

 coloured light when passed into a spectroscope gives a spectrum 

 marked by one or more dark bands, corresponding to the par- 

 ticular rays whose relative retardations in passing through the 

 crystal slice have produced interference. These bands are not 

 always in one place ; they are displaced right ;or left (according 

 to w hether the crystal is a right-handed or a left-handed specimen) 

 if either the analyser or the polariser be rotated. A slice of 

 quartz about 4*3 millims. tliick produces a single band. One of 

 8 '6 millims. two bands at once in the visible spectrum, the 

 number of bands being proportional to the thickness of the 

 crystal. Now suppose a mechanical contrivance by which both 

 the analyser and the spectrum can be rotated at the same velocity. 

 A dij-ect-vision prism attached to the front of the Nicol prism 

 realises the optical portion of this combination. There will be 

 seen on rotation a circular spectrum, having either red or violet 

 at the centre and either violet or red at its outer circumference. 

 Now since the dark band spoken of is displaced by a quantity 

 proportional to the amount of rotation, interference will take 

 place in this circular spectrum along points which form geometri- 

 cally a spiral of Archimedes. The persistence of impressions on 

 the retina will enable this dark spiral to be seen in its entirety, 



