PLATE VII.

_Aphis oenotherae._

FIG. 209. Spermatogonium.

210-211. Spermatogonia in prophase of mitosis.

212. Young spermatocyte of first order.

213. Spermatocytes of first order; conjugation of the chromosomes.

214. Condensation of chromatin--spermatocytes of first order immediately before mitosis.

215. Equatorial plate of first maturation division.

216. Same, side view, showing chromosomes double.

217-218. Anaphase of same mitosis.

219. Daughter spermatocytes of second order.

220. Equatorial plate of second maturation mitosis.

221. Anaphase of same.

222. Young spermatid.

223. Equatorial plate of first polar spindle of winter egg.

224. Equatorial plate of polar spindle of parthenogenetic egg.

225. Equatorial plate of segmentation spindle of parthenogenetic egg.

_Sagitta bipunctata._

FIG. 226. Resting spermatogonia.

227. Prophase of spermatogonial mitosis.

228. Last spermatogonial mitosis, metakinesis.

229. Anaphase of same, showing synapsis of chromosomes at pole of spindle, and element _x_.

230. Resting spermatocyte of first order.

231. Bouquet stage.

232. Later growth stage.

233. Prophase of first maturation mitosis, some of the chromosomes split longitudinally.

234. Later stage, chromosomes condensing and element _x_ dividing.

235-237. First maturation mitosis.

238. Division of element _x_ between the two maturation divisions.

239. Second maturation mitosis.

240. Anaphase of same, showing the element _x_ more deeply stained than the chromosomes.

241. Young spermatids; element _x_ still conspicuous.

[Ill.u.s.tration: STEVENS. PLATE VII.

N. M. S. del

APHIS OENOTHERA--SAGITTA BIPUNCTATA.]