Oct. 1 6, 1879] 



NATURE 



593 



With mixtiu'es of isomorphous salts, however, the results were 

 difierent. In these cases sudden crystallisation on touching with 

 a nucleus producing a separation of both the sulphates apparently 

 always in the proportions in which they existed in the solution. 

 When gi-adual crystallisation took place with the sulphates of 

 nickel and magnesium the nucleus increased by a deposition of 

 the least soluble salt independent of the nature of the nucleus 

 added. It may be seen tlierefore from these experiments that 

 truly isomorphous bodies, that is, substances not only possessing 

 the same form but also an identical chemical structure, may be 

 regarded as active nuclei in exciting the sudden crystallisation of 

 .-upersaturated solutions of each other. I hope shortly to extend 

 the observations upon supersaturated solutions of mixtures, and 

 of compound salts, employing their different 'constituents as 

 nuclei, as I think by such experiments some light may be thrown 

 upon the relations between these constituents when associated 

 together in solution. There are, however, very few true double 

 salts of which it is possible to obtain thorouglily supersaturated 

 s -lutions. John M. Thomson 



OK THE EARLY STAGES OF THE 

 CALCILIANS 



""PHERE are few groups of vertebrates respecting whose 

 ■^ life-history and development so little is known, as the 

 curious snake-like amphibians forming the order Peromela, and 

 usually known as Csecilians. In all the ordinary zoological 

 text-books in use in this country, the early stages of these 

 animals are either left entirely unnoticed, or, at most, allusion is 

 made to Johannes MUUer's classical discovery of gill-slits in 

 the young of Epicrium ghitinostim. Even jProf. Huxley, in 

 hii article on the Amphibia in the first volume of the " Encyclo- 

 paedia Britannica," published in 1875, after an allusion to 

 Miiller's discovery, states : — " It is to be regretted that nothing 

 i< know-n of the development of the Peromela " (foe. cit. p. 770). 

 This being the case, it may be useful to call attention to two 

 papers on the development of the Caecilians, by Dr. Peters, the 

 eminent German naturalist, read by him before the Royal Academy 

 of Sciences of Berlin, and published in their Monatsberichte, as 

 their contents seem to be unknown to, or overlooked by, the bulk 

 r.f English zoologists. The first of these bears the date of 

 January, 1874, .the second was read eighteen months later 

 "(July 19, 1875). In the first of these Dr. Peters, after noticing 

 llie discovery by Miiller of gill-slits in Epicrium, and its sub- 

 ■equent confirmation by himself {cf. Monatsbericht, 1864, 

 p. 303) continues, " it was therefore extremely interesting tome 

 to learn from Prof. Wrzensniowski of Warsaw, who last 

 ijmmer honoured me with a visit, that some years ago the 

 i.aturahst-traveller Constantin Jelski had sent him from Cayenne 

 a gravid Cacilia, which after its capture had given birth to 

 a young one, and had contained in its uterus several full- 

 ;::own embryos. Herr Wrzensniowski has now sent me for 

 i:xamination three of the young ones, and the old animal, re- 

 ferable to Citcilia compressicauda (Dum. and Bibr.), and has 

 :,'ivea with them the following notes, part of w hich are extremely 

 interesting. " These notes are extracted from a letter of Jelski's, 

 dated from Cayenne, November 12, 1866, to Herr Taczanowski, 

 the well-known Polish zoologist, in which he gives his account 

 of an expedition to East Guiana, to a plantation called " Bon 

 Pere," belonging to a M. Lalanne, from which he had just 

 returned. Afternarrating the method of fishing by means of 

 nets adopted, and the great abundance of fish, Jelski continues— 

 " ' In the course of the hunt, the negro w ho was frightening the 

 fi.-U away from tlie bank, suddenly uttered a loud cry : we all 

 .v-v something tliat looked like an electric eel swimming about 

 V. ith worm-like movements just under the .surface of the water. 

 .''I. Lalanne and I held back the negro, who was about to cut the 

 animal into bits with his sword, the net was hauled up, and the 

 creature landed. We all thought it was an eel, but on closer 

 examination decided that it was a gigantic water-worm. I put 

 lUe creature into a special vessel, and as I had already fish 

 enough, and did not hope^to obtain any others, went home. As I 

 was tiiking thi- problematical creature out of the vessel, to put 

 it into the calabash, 1 saw two of them iastead of one. The 

 old one had produced a young one. After I had laid the old 

 one on the talile, I examined it more closely ; it exhibited very 

 slow, tremulous, slight movements. Shortly afterwards I found 

 it in true convulsions. I perceived that it was about to produce 

 a second young one. I placed it in spirit, so ai to convince 

 IJCople of its being viviparous. Membranes (f/Hiile) were 



ejected together with tlie first young one.' Herr Wrzensniowski 

 adds — 'After the receipt of the animal, I dissected it myself, and 

 found in the oviduct five young, w hich I at once extracted,' and 

 two of which I send you together with the one that was bom in 

 Cayenne. All these examples that were removed from the 

 oviducts were remarkable for a membranous outgrowth on the 

 necks which was very easily torn off, and left a transverse linear 

 scar, as in the specimen born in Cayenne, so that only a single 

 specimen has retained this outgrowth till now. In the uterus I 

 perceived nothing else noteworthy ; the embryos lay in a dilata- 

 tion of both oviducts, just as they now are in the spirit, without 

 being covered by any membranous envelopes. I conclude there- 

 fore that the membranes, which, according to Herr Jelski, were 

 extruded together with the young one from the oviduct were 

 nothing else than the shed neck -vesicles (Nackenblase), which we 

 could not find again in the parcel from Cayenne. ' " 



"The female forwarded to me, w hose oviducts had been 

 removed, was fifty cm. long, and four cm. deep in the middle ; 

 its head measured three cm.; of the young ones, the newly- 

 born one, and one of the embryos, had a length of 157 millims., 

 and a depth of twelve millims. ; their heads measured eleven 

 millims.; the other was only 136 millims. long and twelve millims. 

 deep ; its head was ten millims. They show no trace of the 

 skinny vertical swimming-tail {E/osscnsaum) w hich both J. Miiller 

 and myself found on the hinder ends of the young E. glutinosnm. 

 But what surprised me much more was that there was no trace 

 to be found of lateral gill-openings, like those which have now- 

 been discovered in several young examples of Epicrium glutino- 

 sum. The head and fore part of the body in all three specimens 

 lay bent back towards the sides of the belly, so that apparently 

 in the uterus this curved part, that is the under side of the head, 

 is closely applied to the body, and the end of the body also 

 seems to have been recurved towards the sides of the belly. 

 From the neck of the one specimen two smooth vesicles, fifty- 

 five millims. long, of irregular shape, and variously constricted, 

 project ; on them a blood vessel ramifies, whilst at their narrow 

 transverse base they are connected together, thougli unfortunately 

 no more can be learnt as to their original position, except that from 

 their flat convex-concave form they are probably closely applied 

 to the body.' On the transverse scar, where the epidermis is 

 absent, w hich these vesicles leave after falling off, on each side 

 a small hole is visible, the lumen of one or two vessels, which 

 are in connection w-ith the aortic arches of their side. These 

 vesicles therefore are external gills, which resemble the bell- 

 shaped external gills which Dr. Weinland discovered in the 

 larvos which develop in the external dorsal pouch in the 

 female Notoddphys (Opisthodelp/iys) ovifera, and which he 

 has described so well and thoroughly (Miill. Archir, 1S54, 

 p. 457, Taf. xviii., Fig. 5, 6)." After some prefatoiy remarks on 

 the distribution of the vessels to these bladder-like gilk, Dr. 

 Peters concludes: — " In any case, this discovery of a new agree- 

 ment in the development of the Cascilians with the other Batra- 

 chians is one of the greatest scientific interest, for in fact, not only 

 is there now no doubt that, as in the Anura, so also amongst 

 the Ca;cilian3 a diffeYent gill-structure (KicmeitbUdung) obtains, 

 but it can also now be stated with certainty that in these animals 

 also, for which tlie establishment of a third class or sub-class of 

 Amphibians has even been proprosed, no amnion or allantois 

 are developed, that, in part at least, they are viviparous, and 

 that, at a certain period of the year, they are to be sought for, 

 not in moist earth, but in water. Moreover, it is extremely pro- 

 bable that these animals, which only occur to fishermen rarely, 

 and at a certain season, are not recognised by them, but are in 

 fact shunned and destroyed on account of their ugly and worm- 

 like aspect, and on this account so rarely come into the hands of 

 collectors in their larval state." 



In his second pajjer, read July 19, 1875, Dr. Peters contributes 

 some further notes on the same subject, giving figures illustrating 

 the young Ccccilia w ith its bladder-like gills still in situ, as well 

 as the scars left on the neck after the fall of the gills, and the 

 distribution and relations of the great vessels and aortic arches. 

 The bulk of the paper is taken up with an account of the 

 anatomy of the young Caecilians, but a few additional remarks 

 on other ix)ints are given which we here reproduce. "As was 

 there [i.e. in his first paper) stated, in this species the embryos at 

 liirth are at most three and two-thirds smaller than the mother. 

 It is also known that the young of Epicrium glutinosuin, in which 



' ThU i» also very probable from the obser^-alions of Weinland on 

 O^isthodttphyi ffviftra, where the, bcU-shapcd. pUs envelope moit of the 

 body. 



