1. Cambridge strain names The Cambridge strain collection has been renamed as follows: [See Figure 1] 2. A useful aberration on LGIII A stable mutant strain, CB1517, with a severe Dpy e was isolated from the progeny of N2 hermaphrodites treated with 1% acetaldehyde for 2 hours. This strain had peculiar genetic properties, which were eventually explained by Phil Anderson. The strain is homozygous for a large deficiency, eDf2, which removes most of the right arm of LGIII (see map 1979), but it survives because of the presence of a corresponding large free duplication, eDp6(III;f). The duplication is meiotically unstable, so CB1517 produces many inviable zygotes (eDf2 homozygotes), and if CB1517 hermaphrodites are crossed with males carrying a marker in the eDf2 region (say a/+), about 1/3 of the F1 cross progeny are eDf2/a and hence express the a phenotype. This allows rapid assignment of markers to the eDf2 region. The duplication and the deficiency can be separated: eDf2/+ and +/+;eDp6 are essentially wild type in both sexes, though fertility and growth rate are subnormal. The duplication eDp6 is an excellent balancer: I now maintain all tra-1 mutations as tra- 1/tra-1;eDp6 strains, and these strains appear to be completely stable, segregating about 50% tra and 50% tra;eDp6 at each generation. The reason for the Dpy e of CB1517 is not known: it could be due to one or both of the breakpoints at the ends of eDf2, or it could be due to some mutation carried by eDp6. Attempts to isolate other duplication/deficiency strains like CB1517 by acetaldehyde mutagenesis have so far been unsuccessful. 3. Mating efficiency of mutant males I have tested the mating competence of males from most of the standard mutant stocks available in Cambridge. This was done for two reasons: first, it is often convenient to use homozygous mutant males in crosses, so it is helpful to know which mutants can be used in this way. Second, information on male mating efficiency supplements the phenotypic descriptions of the mutants. Some mutations have effects on male anatomy that would not have been expected from the hermaphrodite phenotype. Males were generated by heat shock (hs); backcross (bc) e.g. unc-4 hermaphrodites x unc-4/+ males; from a homozygous male stock (ms) or from a homozygous him stock (hm); or by cross with wild type males (x) for sex linked mutants. Males were tested qualitatively by putting 10 L4/young adult males on a spot plate with 10 unc-17(e245) hermaphrodites (strain CB933). Mating efficiency was scored by rough estimation of the number of cross-progeny produced. [See Figure 2] Percentage scores refer to the quantitative mating assay (see Hodgkin, Horvitz & Brenner, 1979). Males were also briefly examined at 500X magnification to detect anatomical abnormalities. (ts+) means that the mutation is temperature sensitive, and males will mate efficiently if grown at permissive temperature. (-) means that mutant males fail to mature. [See Figures 3-5]