646 SUMMARY OF CURRENT RESEARCHES RELATING TO 



by selection. The mutation theory errs in stating only half a truth. 

 Through mutation and also through the direct action of environment, 

 specific changes may be produced. In another paper * the author makes 

 statistical comparisons of Pectens from the east and west coasts of the 

 United States. 



Muscular Fibres of the Molluscan Heart. — P. Vigier has observed 

 considerable variety in the myocardium of the Molluscan heart. The 

 fibres are sometimes incipiently striated, and sometimes well-striated. 



Those of Anodonta, for instance, are striated fibres of the simple 

 type, such as has been defined by Haswell and Prenant. In Lamelli- 

 branchs generally, it seems that the fibres represent a stage far below 

 that of Arthropods and Vertebrates, and yet above the unstriped level, 

 as is also suggested by their brusque and rhythmical contractions. They 

 recall the embryonic cardiac fibres in the lower Vertebrates. In Cephalo- 

 pods, however, as Marceau has shown, a higher level is attained. 



Arthropoda. 

 a - Insecta. 



Habits of Sphex. J — F. Picard relates in a lively manner his obser- 

 vations on Sphex maxiUosus. This insect is, as regards its habits, still 

 in process of evolution. It is very variable, especially as regards the 

 prey with which it feeds its larvae. It is not so far advanced or " fixed " 

 as some of its fellow-species ; it lingers at an ancestral level. 



Picard reconstructs the history : the first Sphex was in the habit of 

 capturing many kinds of Orthoptera ; gradually the Sphexes began to 

 confine themselves to two or three families, as Sphex maxiUosus does ; 

 later on attention was restricted to one family, as in Sphex albisecta ; 

 subsequently, as in Sphex fiavipennis, operations were confined to a 

 genus ; finally, in the most differentiated species, Sphex occitanica, the 

 prey is a single species, and one sex only. 



The author regards the instinct as an acquired habit, conserved by 

 heredity, transformed little by little in adaptation to external conditions, 

 the modifications being retained or eliminated for the good of the species 

 by natural selection. 



Insect Evolution in Relation to Plants. § — A. Handlirsch notes as 

 factors which have essentially influenced the development of races of 

 insects, (1) the origin of a land flora and fauna in Silurian times ; 

 (2) great climatic alterations during the Permian period (the impulse 

 to the decidedly heterophyletic origin of metamorphoses) ; (3) the 

 appearance of angiosperms in the Chalk. 



Convergence Phenomena in Insects. || — A. Handlirsch points out 

 the frequent occurrence of " convergence " amongst insects, and the con- 

 sequent difficulty of attaining a classification showing real relationships. 

 As instances he quotes the reduction in number of stigmata in aquatic 



* Mark. Anniv. Vol. Art. vi. (1903) pp. 121-36 (1 pi.). 



t Comples Rendus, cxxxviii. (1904) pp. 1534-7. 



j Mem. Soc. Soi. Nat. Cherbourg, xxxiii. (1903) pp. 77-130. 



§ Verb. Zool Bot. Ges. Wien, liv.(1904) pp. 114-9. 



j) Tom. cit., pp. 134-42. 



