The Two Tetralogies

The pantropy series originally had five installments encompassing a beginning, an intermediate stage and a culmination. However, two of the intermediate installments, set on the same planet, were amalgamated when the series was collected as The Seedling Stars, thus generating a tetralogy covering:

experimental colonization of Ganymede;

routine colonization of an extrasolar planet;

three time periods on a planet where the crew of a crashed spaceship have to genetically engineer microscopic human beings to inhabit small pools of water;

a far future culmination when Adapted Men return to the Solar System to recolonize the changed Earth.

The Okie series, four stories with a definite conclusion, were collected as Earthman, Come Home. However, Blish added a prequel, a sequel and a juvenile novel, thus generating a total of four volumes collected in one omnibus volume as Cities In Flight.

The prequel, They Shall Have Stars, jointly novelizes two stories with new material. The three alternating narrative strands cover:

biology, culminating in the anti-agathic drugs;
physics, culminating in antigravity;
politics, culminating in escape from dictatorship.