The endocrine system involves communication by chemical messengers called which circulate through the

Your answers would be Hormones and Bloodstream

hope this helps.  

1. "HORMONES"

2. "BLOODSTREAM"

Explanation:

endocrine glands are the ductless glands which secrete chemical messengers called as hormones ,and these circulate through bloodstream to targeted sites where they inhibit or enhance a function occuring.

the principle of segregation describes how pairs of gene variants are separated into reproductive cells. from his data, mendel formulated the principle of segregation. we now know that the segregation of genes occurs during meiosis in eukaryotes, which is a process that produces reproductive cells called gametes.