In the 6th myotome (i.e. the first with a true segmental tube): 1-2 segmental tubes
In the 7th-10th myotome: 2-3 segmental tubes
In the 11th myotome: 3-4 segmental tubes
In the 12th myotome: 3-4 4-5 segmental tubes
In the 13th myotome: 4-5 segmental tubes
In the 13th-16th myotome: 5-6 segmental tubes
It thus appears that the segmental tubes are not only more numerous than the myotomes, but that the number in each myotome increases from before backwards. In the case of Salamandra there are formed in the region of the posterior (10-16) myotomes secondary, tertiary, etc. segmental tubes out of independent solid cords, which arise in the mesoblast dorsally to the tubes already established.
The secondary segmental tubes appear to develop out of these cords exactly in the same way as the primary ones, except that they do not join the segmental duct directly, but unite with the primary segmental tubes shortly before the junction of the latter with the segmental duct. In this way compound segmental tubes are established with a common collecting tube, but with numerous Malpighian bodies and ciliated peritoneal openings. The difference in the mode of origin of these compound tubes and of those in Elasmobranchii is very striking.
The later stages in the development of the segmental tubes have not been studied in the other Amphibian types.
In Cœciliidæ the earliest stages are not known, but the tubes present in the adult (Spengel) a truly segmental arrangement, and in the young each of them is single, and provided with only a single peritoneal funnel. In the adult however many of the segmental organs become compound, and may have as many as twenty funnels, etc. Both simple and compound segmental tubes occur in all parts of the mesonephros, and are arranged in no definite order.