92 



NATURE 



\_7nnei, 1875 



The results he obtained were not great, but were suffi- 

 cient to enable him to announce that a magneto-electric 

 machine could be constructed which would have the 

 advantage of giving the induced currents all in the same 

 direction, without the help of mechanical arrangements to 

 separate opposed currents or to make them conspire with 

 one another. 



From the foregoing analysis of Pacinotti's memoir, 

 there can be no doubt that it contains a description of the 

 ring armature which in the hands of Gramme has recently 

 led to the construction of magneto- electric machines 

 giving continuous currents of great intensity. I cannot, 

 however, pass over without notice an extraordinary blun- 

 der into which Pacinotti has fallen, and which would 

 render any machine constructed after his model altogether 

 valueless. By a reference to Fig. 2, which, as well as 

 Figs. I and 3, has been engraved from a photograph of 

 the plate appended to the original memoir, it will be seen 

 that the letters N and s are placed at the end of the 

 diameter of the ring which is at right angles to the hne 

 A B joining the poles of the fixed magnet. That Paci- 

 notti intended these letters to designate north and south 

 magnetic poles is manifest from the following passage 

 among others in his memoir : — " Osserviamo che per 

 influenza suUa elettro-calamita mobile si formano i poll 

 opposti alle estremitk di un diametro in presenza ai poli 

 della calamita fissa. Questi poli N S mantengono una 

 posizione fissa anche quando la elettro-calamita trasver- 

 sale ruota sul suo asse." It is hardly necessary to say 

 that the positions assigned by Pacinotti for the poles in 

 an iron ring under the influence of a fixed magnet are in 

 reality those of the neutral points, or points of no mag- 

 netism, and that the magnetic poles of the ring are at a 

 distance of 90° from the positions stated by him. This 

 mistake has led to a serious blunder in the construction 

 of his machine, the metallic rollers which carry off the 

 induced currents being placed, not at the neutral points 

 (as Pacinotti has himself clearly showed that they ought 

 to be), but at the poles of the ring. That any effects at 

 all were obtained from the model at Pisa, we must attri- 

 bute to the slight shifting of the poles of the ring due to 

 its rotation. Apart, however, from this unaccountable 

 error, it can scarcely be disputed that to Pacinotti is due 

 the merit not only of having devised the ring armature 

 or transversal electro-magnet, but of having also accu- 

 rately analysed its mode of action. 



{To be continued^ 



LECTURES AT THE ZOOLOGICAL 



GARDENS* 



V. 



Mr. Garrod on Camels and Llamas 



THE Tylopoda form a group which includes the Camels 

 together with the Llamas ; the name indicating that 

 their feet are covered with callous skin instead of with 

 hoofs as in the typical Ruminants, from which group they 

 also differ considerably in many other characters, to be 

 considered seriatim. 



Horns are not developed in either sex. The upper lip 

 is hairy and partly cleft. False hoofs are wanting. The 

 general body-proportions are not so symmetrical as in 

 any of the Cavicornia or Deer. Osteologically several 

 special features present themselves. In the vertebrae of 

 the neck the canals which are developed in the transverse 

 processes, for the vertebral arteries to run in on their way 

 to the brain, are excavated in the sides of the spinal canal 

 of the cervical region. In the ankle two of the bones — 

 the naviculare, or scaphoid, and the cuboid — which are 

 anchylosed in the true Ruminants, are independent of 

 one another. In the upper jaw there are two teeth deve- 

 loped, one on the side of each premaxilla ; they are there- 



* Continued from p. 69. 



fore lateral incisors. The canines in the lower jaw are of 

 a different shape, and are separated by an interval from 

 the incisors. The molars form a series of five above and 

 four below ; in the Camels, but not in the Llamas, an 

 additional small premolar, isolated in position and follow- 

 ing the canine, is to be found in both jaws, increasing the 

 grinder series to six above and five below on each side. 



The abnormal conformation of the gastric section of 

 the alimentary canal in the Camels has attracted the 

 attention of many naturalists. In the Llamas the same 

 structure maintains. As in the typical Ruminants the 

 stomach is composed of several cavities communicating 

 one with the other, but there is some difficulty in deciding 

 which are the exact homologues of the rtwten, reticulum, 

 psalteritim, and abomasum. The first cavity is a capa- 

 cious globose sac into which the oesophagus opens. A 

 longitudinal band of muscular fibre partly constricts it, 

 in its course from the right side of the cardiac orifice 

 backwards along the ventral surface, opposite the middle 

 of which a narrow and long aggregation of " water cells " 

 starts to continue tranversely towards the left side of the 

 organ. This longitudinal muscular band forms one of 

 the boundaries — the left one — of a much larger collection 

 of deeper water cells, which embrace the posterior portion 

 of the right side of the paunch in the concavity of their 

 crescentic mass. From the right of this first main com- 

 partment a second smaller one is cut off by a constric- 

 tion which leaves a considerable opening between the 

 two. Its position is that of the reticulum ; it is deeply 

 honeycombed, the lining membrane of the cells being 

 covered with villi much like those on the surface of the 

 folds of the psalterium of the deer, &c. The cell-walls 

 are thin and but slightly muscular. In the paunch the 

 mucous membrane is smooth and not at all thick. The 

 water-cells are formed on a framework of many intersect- 

 ing muscular sheets arranged in layers with intervals of 

 less than an inch between them, one half being at right 

 angles to the other, so as to form rows of quadrilateral 

 cavities. These are again incompletely divided up by 

 secondary septa. The orifices of the cells are partly 

 closed by diaphragm-like membranes at their mouths. 

 Most probably the contraction of the aggregated muscular 

 fibres in the same situations is capable of closing the 

 cells completely when necessary. That the camel can 

 store fluid in these water-cells is borne out by the experi- 

 ence of so many authors that doubt is scarcely possible. 

 For instance, in his " Travels to discover the Source of 

 the Nile," Bruce (vol. iv. p. 596) tells us on one occasion 

 that " finding the camels would not rise, we killed two of 

 them . . . and from the stomach of each got about four 

 gallons of water, which the Bischareen Arab managed 

 with great dexterity." As John Hunter remarks, there is 

 no physiological reason why this should not be the case. 

 A specialised structure is observed by zoologists ; a 

 special power is attributed by travellers ; the function 

 and the structure may be reasonably correlated : why 

 should they not be so, as no other explanation suggests 

 itself? There is no arrangement for closing the cells 

 of the reticulum similar to that found in those of the 

 rumen. 



A muscular fold runs from the termination of the 

 oesophagus along the superior or vertebral side of the 

 lesser curvature of the stomach to the third compartment, 

 which evidently directs the products of rumination into 

 it, just as the two folds of the same region do which 

 traverse the reticulum in the typical Peccora. Following 

 the honeycomb-bag is a single elongate cylindrical cavity, 

 which dilates slightly and becomes bent at its pyloric 

 extremity. This compartment is thin-walled and longitu- 

 dinally ribbed internally for its proximal five-sixths, 

 beyond which the mucous membrane is much thickened 

 and evidently digestive in character, especially in the 

 neighbourhood of the angle of the inflection in that region. 

 This section of the stomach apparently corresponds to 



