552 NATURAL SCIENCE. s^p,,. 



than has hitherto been supposed to exist. Here, again, there must 

 be considerable sifting of evidence before a definite conchision can be 

 reached. !Most naturahsts will, however, be startled by Mr. Lowne's 

 comparison of this invagination with that forming the neural canal in 

 vertebrates, a comparison induced by the speculations of Gaskell and 

 Patten that this canal represents an old alimentary tract. The near 

 relationship between arthropods and vertebrates, required bj- this 

 view, will need far more evidence than has yet been produced in its 

 support ; and most students will still prefer to regard a fly and a man 

 as extreme specialisations in very different directions. 



In the Diptera insect-metamorphosis reaches a high degree of 

 specialisation. The organs of the larva are not transformed directly 

 into those of the nymph and imago, but the larval tissues are dis- 

 solved within the pupa, while special invaginations (the imaginal 

 discs) which had been present in the larva, form the pro-nymph. 

 From this the nymph is developed, its external organs being evagi- 

 nated, and it is in turn transformed into the imago. It follows from 

 this that " not one single organ is common to the larva and the 

 imago ; " so " complete " is the metamorphosis, that some observers 

 have regarded it as a case of alternation of generations, considering 

 the nymph as a new embryo. To this somewhat wild suggestion, 

 Mr. Lowne lends no support, but rightly explains it as an extreme 

 case of ecdysis. He refers to the development of the Nemerteans in 

 which the primitive ectoderm is ultimately cast, while the adult 

 skin is formed by invagination from it, as an analogous case. It will 

 be noted that Mr. Lowne speaks of the precursor of the imago as a 

 " nymph," while he uses the term " pupa " for the dried up larva-skin 

 within which the " nymph " is developed. This sense of the words 

 is different from that adopted by entomologists generally. 



The account given of the development of the legs in the nymph 

 deserves special notice. At first there is a basal portion with two 

 processes ; these three parts are compared to the coxopodite, endopo- 

 dite, and exopodite of a crustacean limb. The endopodite becomes 

 five-jointed, and ultimately forms the tarsus. The exopodite 

 lengthens and thickens, finally splitting longitudinally.into a proximal 

 (femur), and distal portion (tibia). The tarsus is, after the split, of 

 course, attached to the tibia. This interpretation is ingenious, but 

 it seems doubtful if the development can have the morphological 

 meaning attached to it by Mr. Lowne, It is remarkable, however, 

 that he and Jaworowski should almost simultaneously have compared 

 respectively the limbs of flies and spiders with those of crustaceans. 



Many of Mr. Lowne's theories will be combated ; some will 

 probably be refuted. He is careful, however, to state clearly the 

 various opinions already put forward on disputed points, and to 

 distinguish between the facts he describes and the hypotheses he 

 builds upon them, A very complete bibliography adds greatly to the 

 value of the work, and future investigators owe a debt of gratitude to 

 our author for his full descriptions of his methods of study which will 

 save them many fruitless experiments, G, H. C. 



Birds : The Elements of Ornithology. By St. George Mivart, F.R.S. Pp. 306, 

 figs. 170. London : R. H. Porter, and Dulau & Co., 1892. Price Cs. 



" This small volume," we are told, " is put forward in the hope 

 of supplying a want which its author has himself felt keenly. It is 

 intended to supply, in a small compass, a general view of the Class of 



