One of my students developed 20 rolls of film the other night. Tonight he was making contact sheets and viewing them with an eye for printing. One roll has very strange "markings" . It looks like someone pre-exposured the film using lizard skin instead of blue sky. then went back and exposed typical shoots. Mostly vacation stuff but nevertheless things he is interested in. THe first thing that came to mind was reticulation, but this is unlike any I have ever seen. Although after 50 years of woerking in the darkroom I haven't seen it happen more than once or twice All film was developed at 68 degrees and the wash water might have gotten to 71 but he is an advanced student and is very careful. I also find it hard to believe that if the temperature had shifted, it only effected one roll. I wish I could do a better job explaning but lizard skins is the best description of the pattern. It is very weak , but easily seen with a lupe and of course no problem with seeing it on the print. Any thoughts would be appreciated. Like to avoid this happening again.