B chromosomes (Bs) are supernumerary to the standard chromosome set, from which they prevalently derive. Variation in numbers both among individuals or populations and among cells within individuals is their constant feature. Leisler’s bat Nyctalus leisleri (Kuhl, 1817) is one of only four species of Chiroptera with detected Bs. Four males of N. leisleri were collected from two localities on the territory of Serbia and cytogenetically analysed. All animals had Bs with interindividual variability ranging from two to five heterochromatic micro Bs. The highest number of Bs was detected in this species. Among mammals, Rodentia and Chiroptera are orders with the largest number of species, but Bs frequently appear in rodents and rarely in chiropterans. Possible explanations for this difference are offered.

中文翻译：

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莱斯勒蝙蝠 Nyctalus leisleri（Kuhl，1817 年）中 B 染色体 (Bs) 数量新高

 B 染色体 (Bs) 是标准染色体组的多余，它们普遍来自标准染色体组。个体或种群之间以及个体内部细胞之间的数量变化是它们的不变特征。Leisler 的蝙蝠 Nyctalus leisleri (Kuhl, 1817) 是仅有的四种检测到 Bs 的翼手目蝙蝠之一。从塞尔维亚领土上的两个地方采集了四只雄性莱斯勒猪笼草并进行了细胞遗传学分析。所有动物都有 Bs，个体间变异性从 2 到 5 个异色微 Bs 不等。在该物种中检测到的 Bs 数量最多。在哺乳动物中，啮齿目和翼手目是种类最多的目，但Bs多见于啮齿类动物，极少见于翼手类动物。提供了这种差异的可能解释。