The first paragraph gives one an idea of the kind of attention that will be required in order to make any sense of what is going on:
"Brand compressed his lips as he realized that once again the woman had taken a place directly behind him in line. She had a place of her own. It wasn't fair. All that whispering, whispering. It made no sense. If she wished an assignation, she could apply to the Bureau. If she hated him, she could get an erase. And if there was no object at all in her attentions, how in Pritchard did she pass her Comp?"
We're on future Earth, or some reasonable facsimile, "post-Era." Society is severely regimented and controlled, and only non-deviant "Units" are permitted on the home world. There they attend School City and learn various specialized tasks that are needed for the proper running of society. Units who don't deviate eventually become Mentors, those who perform the policing function of the world. Deviation is allowed up to a point, and only so many times in the learning process. Once a Unit has exceeded its allotted number of Deviations, they are deemed a failure and sent to one of the five Wilderness Planets, where they will live in crowded conditions, unloved by Pritchard.
Pritchard is evidently the founder of this great class system, a worshiped figure, now long-dead but still followed and living on "forever in the ten billion tubes and circuits of Control." Prichard taught conformity. Prichard taught control. He preached "the Unit which conforms is the Unit most suitable for leadership." He is thought of as an almost godlike entity:
"Pritchard was love. Pritchard was protection... It made him feel good that Pritchard had actually thought of him... as an individual Unit. Pritchard had actually thought of him many years ago, had analyzed his first thought records and destined him to be a School City Mentor..."
That's Brand who is talking, the Unit with the oddly-whispering female behind him in line. She is whispering something that makes absolutely no sense to Brand: "Mary had a little lamb. Its fleece was white as snow..." When she addresses Brand by name, he becomes concerned, but he can't turn around in line because that would be a Deviation. His only hope is that one of the Mentors will hear her, because the whispering itself is a Deviation. Later on they are in line again and she again begins whispering: "There was an old lady who lived in a shoe..." Again, Brand can not turn in line, and can not stop his ears. He realizes that the only way to speak with this woman is to request an assignation in one of the specialized booths designed for such pre-approved activities. He reads her designation number off the back of her tunic and puts in the request. Later on he learns that she has accepted and heads for the booth.
There the woman -- named Doren -- smiles enigmatically and taunts Brand. When Brand attempts to consummate the assignation, Doren won't comply, and Brand leaves the booth infuriated, forgetting to acknowledge the Mentor standing outside.
Busted! It's Brand's last allowed Deviation. "You will now report at once for transportation..."
"Incubation" is all about the growing conformity of society, ratcheted up to the nth degree. It is difficult going at first, but eventually rolls along and is quite understandable. A second reading is a breeze. The editor's brief preface to the story gives the reader a good idea of how things will end:
"Science-fiction writers are not the only ones who are concerned with the increasing mechanization of our society, with the subtle regimentation of our lives, but too many writers have been content to only report it. Too few of them find the passion to condemn it or the will to state that it can be fought. There are times when the inroads of regimentation seem unbeatable -- and it is in such times that writers like John D. MacDonald are needed."
Future Tense is divided into two sections. "On the Record" consists of seven stories that were previously published in science fiction pulp magazines. The second section, "Off the Record," is prefaced thusly:
"Stories which have never before appeared in print in any country. Some of them were especially written for Future Tense, while others failed to please magazine editors for one reason or another."
It's my bet that "Incubation" was one of those in the "failed to please" category, since JDM wasn't a well-known s-f writer of the type who would have been asked for an exclusive submission. In the Acknowledgement section, thanks is given not to MacDonald, but to his agent Cap Shaw.
Future Tense is not impossible to find. Expect to spend some time looking, then be prepared to pay a bit more than you might expect.