6o8 



NATURE 



[Oct. 19, 18S2 



parent shell, moving in the snail's liver. So great is the 

 injury done, that in the laboratory, at any rate, very feu- 

 snails survive three weeks from infection. 



The redia increases in size, and may ultimately reach 

 the length of 1 -3 mm. or about one-twentieth of an inch. It 

 resembles in every respect the redia; I formerly described 

 as found in the same snail at Wytham. Its contents of 

 spherical cells arranged themselves into round germs as 

 in the sporocyst, though I was able in this case to observe 

 the formation of a gastrula. The germs at first were 

 spherical, they then become oval, and afterwards they 

 elongate still more, whilst one end becomes narrower than 

 the other. The narrower end is partiallv constricted 

 from the remainder, and, becoming long and slender, forms 

 the tail of the cercaria, whilst the rest of the germ 

 becomes the body. A sucker appears at the anterior end, 

 and another of nearly equal size at the middle of the 

 ventral surface of the flattened body, whilst within a 

 digestive tract appears. This digestive tract is simply 

 forked, and presents no trace of the lateral branches so 

 ■characteristic of the adult. 



The adult redia contains about a score of germs, but 

 these are in very different stages of development. There are 

 generally two or three nearly mature, the others in various 

 stages down to small spheres of cells. Close to the raised 

 ring surrounding the body of the cercaria there is a small 

 opening as in all redix, by means of which the 

 cercariae are destined to be liberated one by one as they 

 come to maturity. 



But not all the rediae produce cercariae, for they some- 

 times produce other rediae, and these daughter-rediae then 

 give rise to cercariae. These latter, therefore, sometimes 

 only appear as the fourth generation in the snail, and in 

 one set of experiments I had reason to believe that no 

 cercariae appeared earlier. It will thus be seen that a single 

 embryo may give rise to more than a thousand cercariae. 

 In April of the [present year Leuckart published a 

 paper in the "Archiv fur Naturgeschichte," where he 

 described certain experiments on the development of the 

 liver-fluke. He believed that Limnaeus pereger was the 

 intermediate host, and had succeeded in infecting this 

 species, though he had failed to rear the redia beyond the 

 stage in which the contents were forming into spores. He 

 had, however, obtained a number of L. tntncatiiliis from a 

 friend, and had found in them three different sorts of rediae. 

 One of these contained tail-less distomelarvae, and notwith- 

 standing that the characters of the redia were very 

 different from those reared from the embryo of the liver- 

 fluke, he believed the conjecture that this was really the 

 larva of the liver-fluke to be entirely justified until further 

 results were obtained. The second "form he considered 

 might possibly be related to the liver-fluke, but the pro- 

 bability was far less than in the case of the tailless form. 

 In his description of the third form I at once recognised 

 the cercaria I had already found and suggested as the 

 larva of the liver-fluke. Leuckart, however, did not con- 

 sider that there could be any connection, because he 

 failed to detect any spines on the surface of the body 

 such as we should expect, and on account of the lobed 

 lateral organs, which he thought might be the vitellaria of 

 the adult. 



I wrote a report of my own results as described above, 

 giving them, however, in greater detail, for the October 

 number of the Journal of the Royal Agricultural Society. 

 This report was sent to the printer on the 1st of Septem- 

 ber, and a fortnight later received a revision which was 

 merely verbal. 



On October 9th a paper by Leuckart appeared in the 

 Zoologischer Anseiger, a periodical which gives rapid 

 publication to important papers. In this Leuckart ex- 

 tends his former results, and states that he too has reared 

 the cercaria of the liver-fluke in L. truncatulus, and finds 

 that it is the form with the lobed lateral organs which he 

 had already seen, and supposed to have no connection 



with the liver-fluke. It will be seen, therefore, that the 

 cercaria of the liver-fluke is really the form found by me 

 m Limnaeus tnincatulus at Wytham, and described in 

 the Royal Agricultural Society's Journal for 1881. It is 

 interesting to see this result confirmed, not only by my own 

 experiments, but also by Leuckan's independent investi- 

 gations. 



Leuckart has not been able to find any trace in the 

 cercaria of the spines which cover the surface of the 

 adult fluke. He has, however, found in the cells of the 

 cercaria small rod shaped bodies closely resembling 

 bacteria in shape and size, and thinks they may eventu- 

 ally be arranged in bundles and form the spines of the 

 adult. But 1 have already stated that the anterior part 

 of the body of the cercaria is covered with exceedingly 

 fine spines, which can, however, only be seen in the most 

 mature examples. The reason why Prof. Leuckart 

 could not observe these spines was possibly because his 

 examples were scarcely so mature. The rod-like bodies 

 he mentions have certainly no connection with the spines 

 of the adult. He states that they have never yet been 

 found in other cercariae. I may perhaps be allowed to 

 say that they have been described by three -different 

 observers, first by Wagener, then by Filippi in the cercaria 

 of Amphistoma subdavatum, and by myself in the cercaria 

 of the liver-fluke (described in April, 1881. 



For further details of the structure and natural history 

 of the liver-fluke, as well as the discussion of preventive 

 measures, I may refer to my reports in the Journal of the 

 Royal Agricultural Society. 



A. P. THOMAS 



University Museum, Oxford, October 13 



A NEW CASE OF COMMENSAL1SM 



/""VASES of Commensalism amongst the higher animals 

 y^ are rare. Those of the Prairie dog and Rattlesnake, 

 in North America, and of the Burrowing Owl and 

 Vizcacha in the Pampas of Buenos Ayres, are, however, 

 familiar instances of it. The newly issued volume of the 

 " Transactions and Proceedings of the New Zealand 

 Institute" contains a communication from Prof, von 

 Haast on a new and interesting case of two very different 

 animals owning a common habitation. 



One of these creatures being exceedingly scarce and 

 little known, a few details upon this curious subject will 

 be the more acceptable. 



In December iSSo, Mr. Reischek (a correspondent of 

 Prof. v. Haast) paid a visit to a cluster of islands, called 

 the " Chickens " situated East of Wangarei Bay on the 

 East coast of the North Island of New Zealand. These 

 Islands are nowuninhabited by man but contain numerous 

 remains of Maori Pahs and Kitchen-Middens showing 

 that they were formerly much resorted to by the Natives. 



The present inhabitants consist of certain species of 

 birds, of which Mr. Reischek furnishes a list, and of 

 multitudes of the celebrated Tu itara Lizard {Sphenodon 

 t>it 11c tattts)— one of the most anomalous forms of the 

 Lacertian order, if, indeed, we are permitted by Dr. 

 Giinther to call it a Lizard at all. 



Of these birds certain Petrels (namely Pi <occllarta • gouldi, 

 P. Cool-i, and Puffinus gavius) live in holes dug out' by the 

 Tuataras and keep apparantly on the best terms with them. 

 The Tuatara, we are told, excavates its hole mostly on 

 the western slopes of the Islands. The entrance to its 

 chamber is generally four or five inches in diameter, and 

 the passage leading to it often two or three feet long, first 

 descending and then ascending again. The chamber 

 itself is about one foot and a half long, by one foot wide 

 and six inches high and is lined with grass and leaves. 

 The Petrels and Tuataras have their nests separately, one 

 on each side of the entrance, so that they in no way 

 interfere with one another. 



