996 Recent Literature. [December, 



RECENT LITERATURE. 



Lankester on Degeneration. 1 — Mention should have sooner 

 been made of this book, which, with the previously published 

 essay by Dr. Anton Dohrn, 2 draws attention to a phase of devel- 

 opment, which has been somewhat neglected of late years ; 

 although the French naturalists a generation ago had a good deal 

 to say about arrest of development, retrograde development and 

 retrograde metamorphosis. The author recognizes the fact that 

 there are numerous and important exceptions to the general law 

 of progressive development, that some important groups are due 

 to retrogressive development, or to put it into one word, Degenera- 

 tion. Lankester explains what he means by degeneration thus: 

 The lizard-like creature Seps has remarkably small limbs, and in 

 Bipes there is only a pair of stumps, representing the hinder 

 limbs. No naturalist, he says, doubts that Seps and Bipes repre- 

 sent two stages of degeneration, or atrophy of the limbs ; that 

 they have, in fact, been derived from the five-toed, four-legged or- 

 dinary lizard form, and have nearly or almost lost the legs once 

 possessed by their ancestors. 



" This very partial or local atrophy is not, however, that to 

 which I refer when using the word Degeneration. Let us imag- 

 ine this atrophy to extend to a variety of important organs, so 

 that not only the legs, but the organs of sense, the nervous sys- 

 tem, and even the mouth and digestive organs are obliterated, — 

 then we shall have pictured a thorough-going instance of Degen- 



The examples of degeneration given by the author need only 

 to be mentioned, as they are sufficiently striking, and are univer- 

 sally regarded as such. These are the groups of which Sacculina 

 and Peltogaster, Lernaaa and Lepas are examples, The As- 

 cidians are regarded as the result of such a process, and their 

 most important stages of degeneration are represented and 

 briefly discussed, though the figure of the larval Ascidian side 

 by side with the tadpole, on p. 42, is greatly exaggerated, a la 

 Haeckel, and is misleading to the lay-reader. The author also 

 speaks of the Ascidians as if they were universally regarded 

 by zoologists as Vertebrates, whereas they are regarded as Mol- 

 lusks by some, and as worms by many. 3 



The author considers the antecedents of degeneration to be : 

 1. Parasitism; 2. Fixity or immobility ; 3. Vegetative nutrition; 

 4. Excessive reduction in size. . , 



Lankester also regards the sponges as due to degeneration, and 

 " as only somewhat less degenerate we have all the Polyps and 



* Nature Series. Degeneration. A chapter in Darwinism. By Professor E. RAY 

 Lankester, F. R. S. London : Macmillan & Co., 1880. i2mo, pp. 75- Fnce ' '- 1 



2 Der Ursprung der VVirbelthiere und das Princip des Fanctionsvvechsels. Geneal- 

 ogische Skizzen v ipzig, 1875. 8vo, p. 87. 



1 



lutiun, Amer. Naturat ist, 1880, 266. 



