Sentence:  For not only do the antinomies a) to e) disappear when we admit as elements of sets only such sets, <WSD>ordinal numbers</WSD>, and cardinal numbers as are bounded above by a fixed cardinal number, but we see also that paradoxes always arise if we collect into a set any sets, cardinal numbers, or <WSD>ordinal numbers</WSD> which are not bounded above by a fixed cardinal number. 
Meaning of the word marked with <WSD> tags:  Such a number generalised to correspond to any cardinal number (the size of some set); "formally", the order type of some well-ordered set of some cardinality "a", which represents an equivalence class of well-ordered sets (exactly those of cardinality "a") under the equivalence relation "existence of an order-preserving bijection".