196 



NA TURE 



{Dec. 31, 1885 



of the mollusks are thinner than is usually the case with 

 those of the littoral zone ; and Fredericella Duplffsis, 

 which is the representative of F. sultana, has so far 

 varied from the littoral form that it is never found 

 attached to solid bodies, such as pebbles or fragments of 

 coke, but invariably plunged in the soft ooze after the 

 fashion of a Pennatula, 



But of two species of Crustaceans — Niphnrgiis puteanus 

 \'ar. Forelii, an Amphipod, and AscUiis Foivh't, an Isopod 

 closely related to A. cavaiicus — Prof. Forel maintains 

 that they are descended, not directly from the allied 

 species of the littoral zone, but from the species A'- 

 puteanus and A. cavaticus which inhabit the subter- 

 ranean waters, and are commonly found in the wells of 

 nearly the whole of Europe. There is no doubt that A. 

 Forelii is closely related to Asellus nquaticus, nor that 

 Niphargus puteanus is equally closely related to Gam- 

 marus pulexj the question is merely whether the forms at 

 present inhabiting the abysses of the Li^man and other 

 lakes are like Frederitella Duplessis directly descended, 

 or indirectly descended, from the littoral forms. It was 

 to the first of these views that Prof. Forel formerly 

 inclined : he now gives his support to the second. And 

 mainly for the following reasons. The modifications 

 which Niphargus puteanus and TV. Forelii have under- 

 gone are in all important respects the same ; they differ at 

 present only in such unimportant points as the number 

 and length of hairs, seta% and spines. It is unlikely that 

 precisely the same changes would occur under such very 

 different surroundings as those presented by subterranean 

 waters and the deep waters of a lake. Again, N. Forelii 

 is not confined to the L^nian, and it is improbable that 

 exactly the same variations should have arisen in different 

 localities. And thirdly, since maintaining a lacustrine 

 origin for N. Forelii would compel us to admit that it 

 had varied so far from Gammarus pitlex since the Glacial 

 period, we can by supposing it to have a subterranean 

 origin allow it a far longer time in which to have under- 

 gone modification. 



" It is more simple, it is more in conformity with facts 

 to admit that the N. Forelii of our lake-bottoms is de- 

 scended from the N. puteanus of the underground waters. 

 That is the conclusion to which I adhere. And I extend 

 this same conclusion to Asellus Forelii, and seek its 

 origin also in the A. cavaticus of the underground 

 waters." 



An interesting illustration of the manner in which 

 animals can adapt themselves to their surroundings is to 

 be found in the species of Limnea and in the larv» of 

 Diptera (Chironomis) which abound in the L^man. In 

 the littoral zone the Limneas, having a pulmonary sac, 

 are air-breathers ; in the deep water, without any change 

 of structure, their breathing is aquatic — their pulmonary 

 sac is filled with water. The case of the Dipterous larva? 

 is more remarkable. We are told that they swarm in the 

 deep water, and that their respiratory apparatus, consist- 

 ing of tracheae, is, like the sac of the Limneas, filled with 

 water instead of air. Larvae abound, but pupae are very 

 rare, if not altogether absent, and perfect insects are 

 never seen rising from the surface of the deeper parts of 

 the lake ; moreover larv£E of all sizes and ages are found 

 on the bottom at the same season. It would appear from 

 the observations of O. Grimm {Mdm. Acad. imp. St. Pet., 



\v. No. 8, 1S70), of St. Petersburg, that these larva; never 

 attain the perfect stage, but are capable of reproduction 

 by pcedogenesis. 



I have no more space ; I can only allude to the dis- 

 covery of two species of Acanthopus, whose nearest rela- 

 tives are marine Cythrerideffi ; to Plagiostoma Leinani, 

 also with marine relations ; to the remarkable absence in 

 the deep water of Anodon and of Spongilla, both of them 

 so common in the shallows. Let me conclude in Dr. 

 Forel's words : — 



" Others may perhaps regret the absence of the strange 

 things which they had expected to meet with in these 

 strange regions. For my part I have had the intense 

 happiness of being the first to penetrate them, I have 

 endeavoured to explain to inyself one by one the mysteries 

 which unfolded themselves to my gaze, and I admire and 

 enjoy their harmony and their simplicity above all. 

 Nature is beautiful and great because she is harmonious 

 everywhere and in everything." 



G. H. WOLLASTON 



THE CRETACEOUS AND TERTIARY FLORAS 



OF THE UNITED STATES 

 The Cretaceous and Tertiary Floras of the United States. 



By Leo Lesquereux. (U.S. Survey of the Territories 



under F. V. Hayden, Vol. VII.) 

 A FTER an interval of nearly ten years. Dr. Hayden 

 presents us with further contributions, by Lesquereux, 

 to the Cretaceous and Tertiary floras of the United 

 States. Those principally illustrated are from the 

 Dakota, Laramie, and Green River groups. The author 

 frankly admits at the outset, p. 4, that " the determina- 

 tions of the plants are still, and must be for a long time 

 to come, unreliable to a certain degree." This admission 

 must be kept in mind in pronouncing on the merits of 

 the book. 



The Dakota beds rest on Permian, and contain a Cre- 

 taceous fauna associated with a very rich dicotyledonous 

 flora. No one now doubts their Cretaceous age, although 

 they cannot be correlated exactly, bearing in mind the 

 flora, with anything in Europe. It appears from the 

 revision these fossil plants have undergone, that they are 

 much less closely related to existing genera than 

 was previously supposed. Under such circumstances 

 it seems a pity that less compromising generic 

 names were not substituted for those, such as 

 Sassafras, Acer, Ouercus, Hedera, &c., as done in the 

 case of Populites. The known flora of Dakota now con- 

 sists of 5 ferns, 6 Cycads, a dozen Coniferas, most of them 

 very unsatisfactory, and no less than 162 Dicotyledons, 

 chiefly remarkable for the large number of handsome 

 palmate leaves among them. One of the most interest- 

 ing genera, because determined from fruits as well as 

 leaves, is Platanus, a genus also common to our own 

 Lower Eocene of Reading, and thus of a high antiquity. 

 Magnolia is another genus adequately determined, but 

 the remainder rest mainly, if not entirely, on the charac- 

 ters furnished by detached leaves. The vexed question 

 of the age of the Laramie or Great Lignitic series of 

 America is again discussed, and a table given of all its 

 species compared with those of Europe, especially the 

 Eocene of Sifzanne in the Paris Basin. As a result 



