Kelso 最后一次前往 McConnell 位于 Michigan 的旧钓鱼地，带回装满蠕虫的塑胶管，但其中没有一条是学习者。Gershman 说，有一段时间他们大约有 12 种不同品系的涡虫，没有任何一种显示出学习能力。Snyder 说，Kimbles 夫妇完全相信他们在 1960s 的制约实验奏效了，而那个时代的文献似乎也支持他们的确信，因为至少有 36 间实验室报告了类似结果。

Snyder 说，一种解释是 McConnell、Kimbles 夫妇和其他「worm runners」在评分涡虫行为的方式上并不一致，可能把更普通的蠕虫「转向」误解为光反应中明确的「蜷缩」。一个更遥远的可能性是，涡虫本身在过去六十年间因污染或基因漂变而改变，不过 Gershman 认为这不太可能。在 2026，尽管涡虫有神经系统和简单的大脑，它们并不学习；Snyder 说，它们的再生生理保护它们免受钝性创伤，因为被咬成两半后，它们只会重新长回来。

在 2018，University of California, Los Angeles 的 David Glanzman 在训练 Aplysia californica 对尾部电击作出反应后，对其进行了一次记忆移植，透过直接注射遗传物质，将敏化从一只海蛞蝓转移到另一只。2021，Coleen Murphy 发现 Caenorhabditis elegans 这种具有 302 个神经元的微小线虫，可以透过食用或在已经以艰难方式学会的蠕虫泥中游动，学会避开一种致病细菌。Murphy 的团队识别出一种名为 Cer1 的反转座子，似乎能在个体之间携带记忆；几年后，Indian Institute of Science 的一个团队发表了一篇论文，指出受训的 C. elegans 蠕虫会释放细胞外囊泡，能把它们的训练传递给未经训练的同类。

Kelso made one final trip to McConnell’s former fishing grounds in Michigan and returned with plastic tubes full of worms, but not a single one was a learner. Gershman said that at one point they had like 12 different strains of planaria, none of which showed any learning. Snyder said the Kimbles were absolutely convinced that their conditioning experiments in the 1960s had worked, and the literature of the era seemed to support their certainty because at least 36 labs reported similar results.

Snyder said one explanation is that McConnell, the Kimbles, and other “worm runners” were inconsistent in how they scored planarians’ behavior and may have misinterpreted more anodyne worm “turns” for the definitive “scrunch” of the light reaction. A more remote possibility is that planarian worms themselves have changed over the last six decades through pollution or genetic drift, though Gershman finds this unlikely. In 2026, despite their nervous system and simple brains, planarians don’t learn, and Snyder said their regenerative physiology protects them from blunt trauma because, bitten in half, they simply grow back.

In 2018, David Glanzman of the University of California, Los Angeles performed a memory transplant on Aplysia californica after training the slugs to respond to a shock to their tails, transferring sensitization from one slug to another via a direct injection of genetic material. In 2021, Coleen Murphy found that Caenorhabditis elegans worms, microscopic roundworms with 302 neurons, could learn to avoid a pathogenic bacterium by eating or swimming around in pureed worms who had learned the hard way. Murphy’s group identified a retrotransposon called Cer1 that appears to carry a memory between individuals, and a few years later a group at the Indian Institute of Science published a paper suggesting that trained C. elegans worms release extracellular vesicles that can impart their training to naïve counterparts.