No. 625] THE EVOLVTIOX OF AETIIh'OI'ODS 



157 



are with the Isopoda (and Aiiii-liipod;) ). so ilint it i- ])i-of- 

 erable to consider them with tlic hitter moii)!. The Aiio- 

 mostraca-Cumacea group is of the uiTjile-t )»liyl()0(.iH'tic 

 importance, since its members have dc] mitcd as little as 

 any known forms from the prohal)!!' amc-tial condition 

 of the higher Crustacea, Inx'cta aiul "Myriopoda" 

 {seusu lata). 



The Mysidacea have retaiiUMl some primitive charac- 

 ters indicating their connection with the I.ei)tostraca- 

 Hke forms wliicli preceded them, and tlic>- are .|uitc like 

 the ancestors of the encaridan (eni)]iansiacean and deca- 

 podan) members of tlie liigher crustacean grou])s. They 

 are also probably related more remotely to the ancestors 

 of the aberrant hoplocaridan (stomatopodan) line of de- 

 velopment, and through such forms as the Cumacea they 

 are connected with the ancestors of the Tanaidacea (and 

 therefore of the Isopoda also). Tliey are not so impor- 

 tant for a phylogenetic study of the ins(M'ts, (^tc. how- 

 ever, as the Anomostraca and ('ninacca (with tlic Tanai- 

 dacea) are. The Cumacea occupy a i>o-ition interme- 

 diate 1)etween tlie Mysidacea aiul the Tanaidacea. h.Mng 

 somewliat more clos.dy allied to tlie latt.'r. Tliev are 

 also related to the Anomostraca ( Syncai'ida ). a> i^ true 

 of the My>i.lacea, the intenvlation^ of the diff.n-ent 

 UH'mhers of the gnmp being rather complicate.!. 



Ki-om the staiKlpoint cf the >ln.ly of th(^ ].liylou-env of 

 the insects and their relatives the Anomostraca and Cu- 

 macea (together with the Tanaidacea) nr.' by far the 

 most imjiortant forms, since the an.'otor^ of the in-ects 

 aiKl their relatives were (hmlnh-> descended fi'om f..rms 

 closely related to the Anomostraca. CmiKmea. an<l Tanai- 

 dacea. Of the-e three, the Anomo.^ti'aca are a].parently 

 the most ancient (fo»il i'emain> of the other- have not 

 yot Unm fonnd). an.l hav d(mbth'>< departed as little 



The fossil [>lenrocarida' ( c. ./.. ArnHfhnh l..n>i. eti-.) are 

 nearer to the living genera KoouHUf/a, Amisi.idrs, Para- 



