250-251. First spermatocytes, metaphase from mercuro-nitric material. 252-254. Similar stages from Hermann material, showing longitudinal split in both the bivalents, and the odd chromosome (_x_). 255. First spermatocyte, anaphase. 256. First spermatocyte, telophase. 257. First spermatocyte, daughter plates containing 11 and 12 chromosomes, respectively. 258. First spermatocyte, _a_ and _c_ daughter plates, each containing 11 chromosomes, _x_ the odd chromosome at a different level (_b_). 259. Second spermatocyte, equatorial plates of the two classes. 260. Second spermatocyte, metaphase. 261. Second spermatocyte, anaphase. 262-263. Second spermatocyte, daughter plates of the two classes. [Illustration: STEVENS PLATE XIV. N. M. S. del. HEMIPTERA HOMOPTERA] PLATE XV. _Aphrophora quadrangularis._ FIGS. 264-265. Second spermatocyte, telophase, showing chromatin nucleolus (_n_) and the products of division of the odd chromosome (_x_). 266. A spermatid containing the chromatin nucleolus (_n_). 267-268. Spermatids containing both the chromatin nucleolus (_n_) and the odd chromosome (_x_), _a_ the acrosome. 269. Equatorial plate from a somatic cell of a male larva, 23 chromosomes. 270. Equatorial plate of an oögonium, 24 chromosomes. 271. Resting nucleus of a young oöcyte before synapsis, showing two pairs of condensed chromosomes, corresponding in size to the _m_-chromosomes and the odd chromosome of the spermatocytes. 272-277. Sections of nuclei of oöcytes, showing one or more of these heterochromosomes, from safranin-gentian preparations. 278-279. Bouquet stage from iron-hæmatoxylin preparations, showing the heterochromosome bivalent (_x_). _Cacoecia cerasivorana_ (_Lepidoptera_). 280. First spermatocyte, synizesis stage, showing 2 condensed chromosomes (_x_{1}_ and _x_{2}_). 281-282. First spermatocyte, synapsis stage. 283-284. First spermatocyte, growth stages. 285. First spermatocyte, prophase. 286-287. First spermatocyte, later prophases, showing the heterochromosome pair (_x_). 288. First spermatocyte, metaphase. 289. Second spermatocyte, metaphase. 290. First spermatocyte, equatorial plate. 291-292. Second spermatocyte, equatorial plates. _Euvanessa antiopa_ (_Lepidoptera_). 293. First spermatocyte, equatorial plate. [Illustration: STEVENS PLATE XV. N. M. S. del. HEMIPTERA AND LEPIDOPTERA] End of Project Gutenberg's Studies in Spermatogenesis, by Nettie Maria Stevens