How Ncbi Blastn Gets The List Of Organisms Programatically

Hi, Those who use the NCBI BLAST web site recognize the "Choose Search Set" box. After you select OTHER database and you type - in the Organism edit field - an organism name, similar organism names are listed (autocomplete feature). For example type "Bos t"

http://blast.ncbi.nlm.nih.gov/Blast.cgi?PROGRAM=blastn&BLAST_PROGRAMS=megaBlast&PAGE_TYPE=BlastSearch&SHOW_DEFAULTS=on&LINK_LOC=blasthome

Does somebody know which (Entrez?) database are queried and/or parameters used to list the autocompleted names? Sample code maybe?

Cheers