2 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4TH SER. 
CONTENTS—Continued 
PAGE 
TET Mae ration eee ET cial aS cs el Re Rae ear rat eo 22 
Miecration in) the Southern iemisphere.<-0 2.0) pacer 22 
Migration! in the Northern iiemisplere- 4. asses ee eee 24 
Remote Cause of Migrationgenss. seen ssc sae ee eee ee 24 
Immediate: CauseviotsNiierctont arse ore ea | ee yee eee eee ae 25 
OOGs aia RS rc C2 ki ae aac a Meta 1 cage eee 25 
AGTH slesert ect oval spay uA SIA ME De D ne nteen nee Hua IAMC SL MN ernG NAC) lM SG 27 
Cah ber ake) y Va PREM N ION  eoN aia mn li uetinn RC Sigal A OBS ong 29 
Guidance by Old Birdsie eae esis yee eee eee 
Guidance by, Physical Phenomenayaes)-4.e see eerie 30 
EDA Tb eee e Urea coh tha cara eat Val eel a rae a are oe 31 
Summarny.cohy Conclusions! ss ae ya ce anise eine tear ei eae 32 
PW Wieaiatro mtn oe Sune ities od Gane yat ae Oct Uma oe Ria Uc Bianca ued saat fetal 33 
Age, and: Seasonal Vaniatlone ce nis0 ane eet increas naam tans 33 
INVea tT ora ie ee eae Co SL ache acre NC ae eect 33 
Postnatal luma mesa erie cries eed ec cr iets r ainriay kar pure 33 
Mio te Se ee en Ua cee cay ated cet ebawl lade teaser) tet eaatd ct ane 33 
Wear or MPlumagenc: cece ct easter he at ee ciel ahen ol eantlee Aia 34 
1 BAT Dest eG ay entree gua A AN OO aL an Nada Te Ueno CR 35 
Sexialeanduaindivadualm Via nia biomes yan een eres oe eee ee eae 35 
Del oticokoa sha lss rane Seti ein aera iste mon aD I In mule Nene CREM rE Aba ce 36 
Geooraphie Wariationi iss ce a erases. Ata lnc, ua ee ln gies 37 
Wee Classification and. Nomenclature: a5 sere see aera ee eee 39 
General sObservatiOns is ese rose aeie ana rerchseeoere ee eee erate 39 
SPECIES acs di rer ee uae an ne SUAS ood AUNT SIC aU AE Wn a TU 39 
Groupsyote Speciese sae ieee rare sl easel ieee ec er ree Raa 39 
‘The: Subspectes Ouestion josh ee ae ese eee hee 40 
Systematic ACCOUNt es AUN. (ce tacos i Un ot a UR AMR een OR 41 
Mabular Sumimiatyae sees ae eee are aicscean earn ean er eae 68 
VI. Remarks on the Species of the Pacific Ocean Adjacent to North 
Amenica andthe sGalapagos island stiicnemssciurvs tae aie nieraiie na 69 
‘Bix planation Ob) Plate saci cuee car ote cecr arene aes scatte trol arermioielaie eee e cee ae 184 
1 Waa o> cee Sere seo ges Ins AEM aU elem nC MN GLE LAN a Te eee SU ne aah ae Seen aya aca a ate AS 185 
