The imago

Format

A single safetensors file with the .imago extension plus a JSON sidecar, about 300 MB:

• pre_indptr, pre_indices, pre_counts: edges grouped by presynaptic neuron (int64 pointers, int32 indices, int16 counts). Used by the event propagator.
• post_indptr, post_indices, post_counts: the same edges grouped by postsynaptic neuron. Used by the batched propagator.
• Per-neuron arrays: body_id (int64), nt (int8 index into the transmitter table), type_id (int32 index into the type table), superclass_id, side (int8: left, right, unknown).
• Tables in the sidecar: transmitter names, type names, superclass names, build metadata (source file hashes, date, git describe).
• Named neuron sets: photoreceptors with per-neuron eye and column, virtual_photoreceptors, haltere_afferents with side, wing_motor and haltere_motor with side and type, descending.

Transmitter signs

Each synapse’s sign comes from the presynaptic neuron’s consensus neurotransmitter, following Shiu et al.:

Photoreceptor coverage

Coverage of the reconstructed retina map, produced by inferring each photoreceptor’s eye from rootSide and its column from the hex column receiving the largest summed synapse count over hex-bearing targets:

The reconstructed retina is incomplete and imperfectly placed: a real column has six R1-R6 cells, but placed columns hold between one and eleven (v1.0 build, 826 columns with any R1-R6: 240 hold six, 547 hold fewer, 39 hold seven to eleven, the last being placement errors), and 2,054 of the 6,091 photoreceptors have no outgoing edge at all in the significant graph.

Side rule

Sensory neurons carry rootSide and a null somaSide; motor and central neurons carry somaSide and a null rootSide. The imago records somaSide when present, else rootSide. The haltere afferent set keeps each cell’s subclass (haltere 205, campaniform sensilla 195, mechanosensory bristle 39) and type (22 types) as fields, so downstream encoders can group by type rather than by cell.