390 



ISGIENCE. 



[N. S. Vol. XI. No. 271. 



grasp the most important point brought out by 

 Brauer. He says (p. 175) that one of the chief 

 characters on which Brauer bases his system is 

 tlie existence or absence of wings ; and later 

 (p. 176) he says "Thus it (Brauer' s classifica- 

 tion) begins by a division of Insecta into winged 

 and wingless ; but the winged division is made 

 to comprehend an enormous number of wing- 

 less Insects, whole subdivisions of Orders such 

 as Mallophaga being placed in the winged 

 series, although all are without wings." Now 

 the fact is Brauer does not use the existence 

 or absence of wings as a character distinguish- 

 ing the two groups into which he divides the 

 Insecta. Brauer believes that the wingless con- 

 dition of the Thysanura and Collembola is due 

 to their generalized condition ; that none of their 

 ancestors had wings. On the other hand 

 he believes that the wingless condition of 

 all other wingless insects is a secondary 

 condition, that they have descended from 

 winged ancestors. In other words that exist- 

 ing insects represent two distinct lines of de- 

 scent ; in one, the primitive wingless condition 

 has been constantly retained ; in the other are 

 found only descendants of a common-wiuged 

 ancestor. This distinction is clearly indicated 

 bj' the names he proposed for the two groups, 

 Apterygogenea and Pterygogenea. The fact 

 that many of the Pterygogenea have lost their 

 wings does not militate in the least against 

 this distinction. The onlj' indication that our 

 author has understood Bravier's position is a 

 statement that " This first division is entirely 

 theoretical." But if we give him credit for 

 understanding Brauer we must blame him for 

 stating the case in a very misleading manner. 

 As a rule, however, the work is written in a 

 clear, simple style. The illugtrations are abun- 

 dant and are excellent ; and the pages present 

 an attractive appearance. It is a work that no 

 entomologist can afford to be without. 



J. H. COMSTOCK. 



Traite de Zoologie Concrke. By Yves Delage 

 and Edgaed Herouaed. Tome 11, Ire 

 Partie, Mesozoaires, Spongiares. Paris, 

 Schleicher Freres. 244 pages 15 colored 

 plates and 274 text figures. 1899. 

 In the most recent volume of their ' Concrete 



Zoology ' Delage and Herouard present, from 

 the teacher' s standpoint, one of the most difficult 

 branches of Invertebrate Zoology, and only 

 praise is due them for the excellent manner in 

 which the subjects are treated. 



The group including the two families Dioye- 

 midse and Orthonectidse, to which Van Beneden 

 gave the name Mesozoa as indicative of their 

 supposed intermediate position between the 

 Metazoa and the Protozoa is considerably en- 

 larged by the addition of a number of forms 

 which show less evidence of degeneration than 

 do Van Beneden's original types. The classi- 

 fication, however, is only provisional, for in 

 most cases the life history is not known and it 

 is recognized that future investigations may 

 show the forms in question to be only larval 

 stages of other animals. With this in mind the 

 authors make four classes of the Mesozoa as 

 follows, the name of each class indicating the 

 nature of the sub-ectodermal structures : (1) 

 Mesocoelia. — Forms having a digestive cavity 

 with no other cellular boundary than the ecto- 

 derm (Frenzel's SaUnella salve). (2) Mesen- 

 CHYMIA. — Forms having a parenchymatous 

 tissue within the ectoderm and without a diges- 

 tive cavity {Trichoplax and Treptoplax (Monti- 

 celli)). (3) Mesogonia. — Forms without di- 

 gestive cavity and with one or several cells 

 beneath the ectoderm which are destined for 

 sexual reproduction (Dicyemidfe and Orthonec- 

 tidse). (4) Mesogastbia. — Forms having a 

 digestive tract like the archenteron of a gast- 

 rula, the walls being separated from the ecto- 

 derm by a coelomic cavity in which there is no 

 intermediate tissue {Pemmatodiscus, a parasite 

 on JRhizostoma pulmo (Monticelli)). In addition 

 to these classes, Haeckel's Physemaria, the 

 ' urn' forms in the cavities of the Sipunculidte, 

 and the curious form described by Caullery and 

 Mesnil under the name Siedleckia nematoides, 

 are included as appendices. 



In the second part of the volume the authors 

 put into their subject an intimate knowledge 

 gained only by personal investigation and con- 

 tinued research upon the structure and the de- 

 velopment of the Sponges. The result is a 

 clear and concise presentation of the numerous 

 complicated Sponge-structures. The canals, 

 inhalent and exhalent, with their many con- 



