DB0BMBEE21, 1900.] 



SCIENCE. 



963 



not extraordinary. Weismann, having placed 

 the larva of Musca vomitoria under water, has 

 seen that the tracheal system remains filled 

 with air at the expiration of several hours. 

 The respiration of internal larvae is then very 

 normal, the tracheal system having undergone 

 slight modifications. Upon leaving the host 

 the spiracles open and the air enters through 

 them. 



(c) Molts. — He has observed a molt in the 

 young internal larva of Apanteles glomeratus. 

 The mandibles and the larval cuticle are shed. 

 In certain of the young larvae, one sees, in fact, 

 after the molt of the body, the two mandibles 

 of an earlier stage. The molt is made like that 

 of the pupa, the old skin slipping from before 

 towards the anal end of the body. The larva 

 sheds this old skin into the open space behind it. 



Such are the facts concerning the mode of 

 life of internal parasites in their hosts. There 

 is really nothing mysterious in this mode of 

 life. The functions are accomplished normally 

 by means of slight modifications which it would 

 have been easy to foresee. 



M. Seurat is heartily to be congratulated on 

 this excellent piece of work, setting at rest, as 

 it does, so many mooted points. It is interesting 

 to note that he has not made any observations 

 at all parallel to those of Marchal, who states 

 that a single egg of Encyrtus laid in the egg of 

 Hyponomeuta dissociates itself into a great 

 number of embryos which develop into indi- 

 vidual larvae in the larva of the host. 



L. O. Howard. 



The Structure and Life-History of the Harlequin 

 Fly (Chironomus). By L. C. Miall, F.R.S., 

 and A. E. Hammond, F.L.8. Oxford, Clar- 

 endon Press. 1900. Pp. 191 ; figs. 129. 

 Professor Miall has gained an enviable repu- 

 tation as a student of the life history and struc- 

 ture of a number of common insects, and in the 

 course of this work he has discovered many 

 novel and important facts. His little book en- 

 titled ' The Structure and Life-History of the 

 Cockroach,' done in collaboration with Alfred 

 Denny, is a model treatise on Orthopteran in- 

 sect anatomy and his treatise on ' The Natural 

 History of Aquatic Insects ' is one of the most 

 valuable and readable entomological books 



which has been published of late years. In the 

 present volume the authors have given a very 

 careful study of the development of the Chir- 

 onomidae, some of the species of which have 

 long been favorite objects with histologists and 

 embryologists. They have a very special biolog- 

 ical interest in their various stages and it is 

 thought that their inclusion in ordinary teaching 

 courses will be desirable and will be facilitated 

 by the present volume. Chironomus larvae are 

 very abundant and are found in pools and 

 streams and at the bottom of deep fresh water 

 lakes. Professor S. I. Smith having dredged them 

 from the bottom of Lake Superior at a depth of 

 nearly 1,000 feet. They have also been found in 

 salt water and Packard has studied a species 

 abundant at low water mark in Salem Harbor. 



The larvae inhabit tubes which they make of 

 silk and mud or aquatic vegetation, and certain 

 of the larvae possess only a rudimentary tracheal 

 system which appears late in the larval stage. 

 No insect known to the writers has more com- 

 pletely departed from the habits and structure 

 of an air-breathing animal, yet even here is 

 found proof of descent from a terrestrial insect 

 with branching air tubes. This remarkable 

 modification is necessary from the fact that 

 certain of the larvae live at great depths where 

 it is impossible for them to rise to the surface. 

 This absence of a tracheal system does away 

 with the possibility of breathing by tracheal 

 gills which is the commonest respiratory method 

 with aquatic insects and necessitates the pres- 

 ence of blood gills, so that respiration is accom- 

 plished practically as with fishes and larval 

 Batrachea. 



The whole internal anatomy of all stages is 

 carefully described, with excellent figures, and 

 this is done in a masterly and comparative way 

 and includes a study of the embryonic develop- 

 ment. An appendix is devoted to the methods 

 of anatomical and histological investigation. 



An important point which the authors bear 

 in mind and which Professor Miall has fre- 

 quently advanced is that they desire by such 

 work to incite the members of naturalist clubs 

 and other non-academic biologists to take up 

 the study of life histories. Such work in the 

 past has yielded facts of the greatest biologic 

 importance, and yet to-day the field is largely 



