Photolysis of 1,3,4-trimethyl-1-phenylgermacyclopent-3-ene (5) in hydrocarbon solvents containing isoprene, methanol, or acetic acid affords 2,3-dimethyl-1,3-butadiene (DMB) and the expected trapping products of methylphenylgermylene (GeMePh) in chemical yields exceeding 90%. The germylene has been detected in hexane solution by laser flash photolysis, as a short-lived species (t ~ 2 ms) exhibiting a UV/vis absorption spectrum centered at l_max = 490 nm. It decays with second-order kinetics and a rate constant close to the diffusion-controlled limit, with the concomitant growth of a second, longer-lived transient (l_max = 415 nm) that is assigned to a mixture of E- and Z-1,2-dimethyl-1,2-diphenyldigermene (4). Absolute rate constants have been determined for reaction of the germylene with primary and tertiary amines (n-BuNH₂ and Et₃N, respectively), acetic acid (AcOH), a terminal alkyne and alkene, isoprene, DMB, CCl₄, the Group 14 hydrides Et₃SiH and Bu₃SnH. GeMePh is slightly more reactive than GePh₂ towards all the reagents studied in this work; both are significantly less reactive than GeMe₂ toward the same substrates. Absolute rate constants for reaction of 4 have also been measured or assigned upper limits in every case, and are compared to previously reported values for tetraphenyl- and tetramethyldigermene with the same reagents.