The space amoeba optical effects were created by Frank Van der Veer of Van der Veer Photo Effects. The amoeba itself was a mixture of liquids pressed between two thin sheets of glass. As the sheets were moved, the liquid would flow, as if the amoeba were pulsating.
The same technique was used to present "psychedelic" light shows in the late 1960s when bands were playing at venues such as the Fillmore West and the Avalon Ballroom in San Francisco.
The same technique was used to present "psychedelic" light shows in the late 1960s when bands were playing at venues such as the Fillmore West and the Avalon Ballroom in San Francisco.
This is the last episode directed by Joseph Pevney who, along with Marc Daniels, holds the record for directing the most number of episodes for the series (14).
This is the last time the interior of a shuttlecraft is shown in the series.
This was what is known as a "bottle" episode, which is often done to save money. Star Trek was often at odds over its budget and often exceeded it due to special effects and set constructions. The network insisted they produce a "cheap" episode to save money. This one had no expensive guest stars (which saves a lot of money), no outdoor location filming, and no new set construction, and therefore came significantly under budget.
This was the last time in which Kirk's green wrap-around tunic was used. The last time viewers would see the shirt would be in Bread and Circuses (1968), which had been filmed earlier but not aired for almost a year.