Sentence:  The "swallows" especially must do great work in the case, if we take into their number not only very many open gulphs or chasms, the depth of which no line or sound can reach; but likewise the "communications" of very many "parts of the sea", and of many great "unfathomable lochs", with the "abyss". These <WSD>"absorbers</WSD>" could easily receive what had before come out of them. 
Meaning of the word marked with <WSD> tags:  Something that absorbs.