Table 1.

Summary of the contact site quantification of the FIB-SEM datasets.

Age group	Total n of contacts	Filopodial contact		Flat contact		Fusion site
		Av. length, z	n	Av. length, z	n	Av. length, z	Av. length, xy	n
P15/16	36	114 ± 17.4 nm	32	42.3 ± 3.70 nm	3	35.0 nm	136 nm	1
P34/37	23	198 ± 7.50 nm	2	1.69 ± 0.57 µm	14	27.9 ± 6.53 nm	69.3 ± 20.6 nm	7

Summary of the total number of contacts, of filopodial contacts, flat contacts, and putative fusion sites as well as of their average length in z-plane. Note, that we excluded one putative fusion site depicted in Fig. 5e, from the statistics of the P34 data as an outlier, as the z-measurements of 535 nm clearly exceeds 1.5 times the interquartile range above the third quartile (75th percentile). Further, the maximum extent of the cytoplasmic bridge of putative fusion sites was measured in the xy-plane using 3dmod, as indicated in Supplementary Table 1, and averaged. For the age-group of P15/16 only 1 example for a fusion site was found and the respecting values are listed in the Table. Data are presented as mean ± S.E.M. P15/16: n = 3 FIB-runs (2 FIB-runs from P15, 1 FIB-run from P16) each with 1 full IHC and the respective contacts to neighboring IHCs, N_animals = 2. P34/37: n = 3 FIB-runs (2 FIB-runs from P34, 1 FIB-run from P37) each with 1 full IHC and the respective contacts to neighboring IHCs, N_animals = 2. Per age group 2 independent embeddings were performed.