s.

240. First spermatocytes, very early growth stage, _x_ the odd
chromosome.

241-243. First spermatocyte, later spireme stages, showing the odd
chromosome (_x_) and a pair of _m_-chromosomes (_m_).

244. Similar stage from a safranin-gentian preparation.

245. First spermatocyte, split-spireme stage, _x_ the odd chromosome,
_m_ the _m_-chromosome tetrad.

246. Similar stage from a safranin-gentian preparation.

247-248. First spermatocyte, condensation of chromatin granules to form
tetrads in the linin spireme.

249. Later tetrad stage.

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 oogonium, 24 chromosomes.

271. Resting nucleus of a young oocyte 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 oocytes, showing one or more of these
heterochromosomes, from safranin-gentian preparations.

278-279. Bouquet stage from iron-haematoxylin 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