No. G25] THE KVOlJ 'noX OF AUTllUOPODS 



159 



(and also related to the Mysidacea), so that the sessile- 

 eyed character occur rinj:>- in the j>Tonp might be regarded 

 as a retention of the tendency toward the formation of 

 sessile eyes exliibited by sncli primitive forms as Koo- 

 nunga, while the slender body form present in such Am- 

 phii)oda as the caprellids, Rhahdosoma, etc., may possi- 

 bly be due to the retention of the tendency toward the 

 slender form of body (such as that ])resent in the more 

 primitive Bnthynella) in forms which are otherwise rather 

 higlily modified. Tlie Isopoda-Amphipoda group origi- 

 nated very close to the point of origin of the insect line 

 of development, and the two lines have paralleled one 

 another extremely closely. Since the* members of the 

 Iso]->oda-Am])hipoda group have not travelled so far 

 aloim- the inith of specialization in following the same 

 developmental road with the iii-ect<, they have retained 

 many primitive feature^ characteristic of the ancestors 

 of the insects (and "myriopods"), and such forms as 

 Apsnides^ are particularly interesting for a phylogenetic 

 study of insects and their immediate relatives. 



Tlie Svm])hvla-Panro])oda grou]-) (composed of such 

 form^ S< ,,inpnuh > lii , S, nl m, , rlia . I^onopu., K,tru- 

 p>iHjn,ni^, and tlicir iinnitMliatc ivlali\.-) cnritniii- the 

 fornix ^v]^n•ll m.pear to he very near tiie of tlie 



''myriopoit" stem, and wliicli have retained a great num- 

 ber of features characteristic of the ancestors of insects, 

 so that a study of the structures of the Tsopoda-Amphi- 

 l>oda group and the Synii)hyla-Pauro]ioda group are of 

 the greatest inii^oi'tanc*- foi' a prop^M- conception of tlie 

 nature of the lir-^t in-c.-t^ to ho oxohed. The Syni].]iyla- 

 Pauropoda gi-ouj) |irobnltiv also arose from forms occu- 

 pying a i)osition int(M'nie<liate between the Anomostraca 

 and Cumacea. and likewise closely related to the Tanai- 

 dacea which originated from similar forebears. Such 

 Anomostraca a- h'afln/tnlhi hn\e not de})arted far from 

 the ancestral c(»n(lition of llit^ Synipliyla-Pauropoda 

 group, and altlioiiuli ilu-\ lia\e developed niany modifi- 

 cations along their own line of si)ecialization, they are as 



