422 K- and 13 ∑--capture stars emitting mesic hyperfragments (MHF) have been studied in an attempt to understand the mechanism of hyperfragment production. 123 K- stars emitting8Li fragments were also considered. Several criteria were used to separate K- captures in C, N, O and Ag, Br. Lower limits for the proportion of MHF produced in C, N, O are 57%, 73%, 84%, and 94% for HΛ, HeΛ, LiΛ and MHF of Z ≥ 4. For8Li, this lower limit is 75%. An overall frequency of (1.05±0.05)·10-2 MHF/K--capture and (3.8±1.4) · 10-2 HF/∑--capture is obtained. The energy spectrum of the pions emitted in the capture stars indicates that a substantial fraction of the emitted bound Λ’s originates in ∑-conversion processes. Indication of bound-Λ production from multinucleon K--capture processes was obtained, important in the case of HΛ. The momentum spectra for different hypernuclear species are very similar and the spectra of HeΛ and LiΛ are, in turn, comparable with the momentum spectra of He and8Li respectively. Hyperfragments are emitted preferentially opposite to the direction of emission of an associated pion or fast proton. The backwards-forward (B/F) ratio is for π, MHF events, 1.8±0.4. Two models for the production of hyperfragments are proposed. According to the first (« trapped-Λ ») the Λ created in the elementary process is trapped in the nuclear potential well of the parent nucleus. The HF is then emitted in the process of nuclear de-excitation. In the second model (« prompt-HF ») the HF is emitted promptly following the K- or ∑- interaction with a group of nucleons. It is concluded that both mechanisms may contribute. The occurrence of both processes can explain essentially all the salient features of hyperfragment emission.