Oct. 4, 1877] 



NATURE 



475 



LETTERS TO THE EDITOR 



[Tht Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 

 The Editor urgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the appearance even of com- 

 munications containing interesting and novel facts. ] 

 Urticating Organs of Planarian Worms 



There exist, as is well known to all comparative anatomists, 

 in the skin of most planarian worms certain rod-like bodies 

 (Stabchenkurperchen of German authors) concerning the function 

 and homologies of which there has been consideiable speculation 

 and difference of opinion. By some authors these bodies, which 

 always at an early stage of their existence are contained in cells, 

 "the rod-cells" have been compared to the thread-cells or 

 nematocysts of coelenterata, the rod-cells being considered 

 homologous to or possibly homogenous with these coelenterate 

 nematocysts. In the July number of the Quarterly Journal of 

 Microscopical Science, vol. Ixvii., new series, 1S77, I published a 

 paper on the structure of several forms of land planarians obtained 

 by me during the voyage of II. M.S. Challenger. In this paper 

 is described and figured the structure of the rod-cells of several 

 genera of land planarians as observed in the fresh and living 

 condition. In an American form Geoflana flava and also in a 

 Ceoplana from New Zealand and a Rhynchodemus from the Cape 

 of Good Hope rod-cells were observed in which the rods are 

 much longer than the cells and are in their quiescent condition 

 coded spirally within the cells {I.e., PI. xx. Figs. 15, 20, 21, 22, 

 23), but which rods are shot out from the cells and protruded for 

 a long distance beyond the surface of the epidermis when the 

 animal is compressed or irritated. Such probably is the mature 

 condition of the cells in question in all land planarians. 

 Mecznikow has described a somewhat similar form of cell as 

 exisfintj in his Geodesmus bilin^atus. 



In sone microscopic sections of land planarians hardened in 

 alcohol, the shot-rods or threads may be seen in abundance 

 when closely looked for, projecting from the edges of the section 

 of the epidermis. The demonstration of the spiral coiling of 

 the rods within the cells, and of their protrusion on irritation, 

 would at first sir;ht seem to ally these bodies more closely than 

 ever with ca;lenterate nematocysts, but there is this great differ- 

 ence between the two structures, that several rods are present in 

 each cell in the planarians, and that the rods are solid and 

 apparently free within the cell, and when protruded by the 

 bursting of the cell are shot clear of it. In crelenterates, as is 

 familiarly known, the thread is continuous with the cell and 

 hollow, and is everted in the act of protrusion. 



In the summary of ray paper above referred to (I.e., p. 292) I 

 suggested tliat it would be interesting to test the action of the 

 rod bodies of land planarians by applying a living worm to the 

 tongue and observing whether urtication was produced. I wrote 

 at the time to my friend, Mr. Thwaites, F.R.S., curator of the 

 Royal Botanic Gardens at Peradeniya, Ceylon, and asked him 

 to make the experiment, which he did forthwith, and the result 

 shows that planarians do undoubtedly produce urtication in much 

 the same way as ccelenterates, and there can be no doubt that 

 this function is performed by the rod-bodies, which are thus 

 weapons of defence, and no doubt used also to secure prey. 



Mr. Thwaites writes : — " I have lost no time before attending 

 to your request touching the planarians. I applied the tip of 

 my tongue to two of them brought fresh and lively to me, and 

 quite sensible was I to a feeling of unpleasant tingling, and it 

 was accompanied with slight swelling. The sensations very 

 similar to what is experienced upon a slight scalding. The 

 planarian itself evidently felt very uncomfortable, as it became 

 dilated laterally to a considerable extent during contact with the 

 tip of the tongue, though it soon recovered its normal condition." 



H. N. MOSELEY 



New University Club, St. James's Street, S. W. 



The Satellites of Mars 

 It seems worthy of notice that the prophetic genius of Homer 

 has already not only identified but even given names to the two 

 satellites of Mars. I allude, of course, to the passage in the 

 fifteenth book of the Iliad, where Ares is preparing to descend 

 to the earth (possibly this refers to an unusually near approach 

 at opposition, as at the present time) : — 



*ns fpaTO'Kai ^' 'hTTovs Ki\fTO Afiu.il* Te 'i'S^oy Tf 

 ^evyvuij.d'. . . II., XV. 1 19. 



which Pope renders — 



" With tliat he gives command to Fear and Flight 

 To join his rapid coursers for the fight ."^ 

 Deimus and Phobus are not, perhaps, very euphonious names ; 

 but astronomers will not lightly reject the authority of Homer. 

 Eton, September 29 H. G. Madan 



On the Coming Winter 



Having recently computed the remaining observations of cur 

 earth-thermometers here, and prepared a new projection of all the 

 observations from their beginning in 1S37 to their calamitous 

 close last year — results generally confirmatory of those arrived 

 at in 1S70 have been obtained, but with more pointed and 

 immediate bearing on the weather now before us. 



The chief features undoubtedly deducible for the past thirty- 

 nine years, after eliminating the more seasonal effects of ordinary 

 summer and winter, are : — 



1. Between 1S37 and 1876 three great heat-waves, from with- 

 out, struck this part of the earth; viz., the first in iS46'5, the 

 second in 185S0, and the third in 18687. And unless some 

 very complete alteration in the weather is to take place, the 

 next such visitation may be looked for in i879'5, within limits 

 of half a year each way. 



2. The next feature in magnitude and certainty is, that the 

 periods of minimum temperature, or cold, are not either in, or 

 anywhere near, the middle time between the crests of those three 

 chronologically identified heat-waves, but are comparatively 

 close up to them on either side, at a distance of about a year and 

 a half, so that the next such cold wave is due at the end of the 

 present year. 



This is, perhaps, not an agreeable prospect, especially if political 

 agitators are at this time moving amongst the colliers, striving 

 to persuade them to decrease the out-put of coal at every pit's- 

 mouth. Being, therefore, quite willing, for the general good, 

 to suppose myself mistaken, I beg to send you a first impression 

 of plate 17 of the forthcoming volume of observations of this 

 Royal Observatory, and shall be very happy if you can bring 

 out from the measures recordedthere, anymore comfortable view 

 for the public at large. PiAzzi Smyth 



Astronomer- Royal for Scotland 



Royal Observatory, Edinburgh, September 27 



The Australian Monotremes 

 I OBSERVE in Nature (vol. xvi. p. 439) that a doubt arises 

 respecting the Echidna or Australian porcupine (recently re- 

 named Tachyglossus) and the Ornithorhynchus being found in 

 Northern Australia. It does exist in Queensland, but how far 

 north it is impossible to decide until we are better acquainted 

 with that extensive territory. The fact of one having been found 

 by Mr. Kennedy, as mentioned by Mr. Forbes at Plain Creek in 

 lat. 21° S. is, as far as the published statement can be depended 

 upon, correct, and was never considered by any Australian in 

 Queensland as a matter of doubt, as they were well acquainted 

 with the animal ; but whether the Tachyglossus was the same or 

 of a different species I do not consider has been suiiBciently 

 noticed ; whether it was the Tachyglossus hystrix, or with suffi- 

 cient distinctive characters, as has been recently found in that ol 

 New Guinea to niake it a new species, is not known, as ordinary 

 travellers are not able to distinguish those characteristic difler- 

 ences which would immediately strike the experienced naturalist. 

 The species found in the vicinity of Darling Djwns, &c. , is 

 evidently the Tachyglossus hystrix, and from a recent letter 

 received from my son, Mr. G. F. Bennett, he I5nds no difficulty 

 in procuring specimens of this species near Foowoomba by offer- 

 ing rewards for those procured at certain intervals of time, to 

 enable him to carry out his investigations on the mode of 

 generation of the Monolreinata, and if possible to procure the 

 impregnated uterus of that animal, as well as that of the Orni- 

 thorhynchus, as in both animals it no doubt will be identical. 

 As far as regards the rudimental pouch in the Echidna it 

 is only ab'e to be found in that animal during the breed- 

 ing season, and I could never detect it at any other time. 

 It is mentioned by Prof. Owen in his memoir on the young 

 of the Echidna {Philosiphical Transactions, 1S65, p. 67S), and 

 indeed it has been a well-known fact for some period of time, as 

 some years ago I doubted the assertion and public attention was 

 most particularly drawn to it, and the fact was ascertained 

 beyond doubt even before the publication of Prof. Owen's paper. 



