OCR Text |
Show 322 MR. M. F. WOODWARD ON THE [Mar. 28, examination of these under a high power showed them to consist of a large amount of lightly staining protoplasm, w ith an enormous central nucleus, whose chromatin was aggregated into one immense nucleolus, staining darkly, while the nucleus itself remained practically unstained. The general structure of these cells at once suggested ova, and on a careful comparison with the normal ovum (Plate X X I V . fig. 5 a, b), it will be seen that it is impossible to distinguish the large cells of this accessory gland from ripe ova and the few moderate-sized cells from developing ones L Thus w e have in this specimen situated on the 11/12 mesentery, just above the coiled portion of the vas deferens, on the right side a body indistinguishable from a testis, and on the left side one consisting of a ground-mass of testicular tissue, in which are imbedded a few undoubted ova. In other words, we have here on the left side a true hermaphrodite gland, comparable in all its essentials to the ova-testis of a hermaphrodite mollusk, and, like that, budding-off sperm mother-cells into the ccelom, the ova remaining adherent to the wall of the gland until fully formed. In most hermaphrodite invertebrates known the male and female genital glands are quite distinct from one another; in fact it is only in some Mollusca and a iew Crustacea where we find genuine hermaphrodite glands. Bernard has described such a condition in Apus 2,where spermatozoa were developed in the ovary ; and Ishikawa3 has discovered the constant presence of ova in the posterior part of the testis of Gebia. W e have now recorded this condition in a third group of Invertebrata, viz. the Chaetopoda. Leaving on one side the question as to a probably hermaphroditism of the ancestral worms, we may safely regard the ova and sperm mother-cells, the ovaries and the testes as a whole, as being homologous structures among the Oligochaeta, for we have seen that ovaries or testes may either develop indifferently upon mesentery 11/12 or be replaced by a true hermaphrodite gland. I have already pointed out (I. c. p. 187) that ovaries may occasionally be developed on the mesenteries 11-18, and now I have only to record the fact that the presence of additional ovaries is much more frequent than has been supposed, especially on mesentery 13/14 (figs. 1 aud 6, ov2) and not unfrequently on 11/12. A very curious condition in the development of an ovary is seen in the specimen under notice, wdiere a mass of ova, mature and immature, was found iu a special cavity surrounded by a thin epi-theloid capsule, to which the eggs were attached, immediately under 1 There seemed just a possibility that these large cells might be encysted Gregarines, and, in order to settle this question, sections were made of the ovary of an Earthworm which bad a number of these parasites encysted withhi it. Tbe difference between these cells and the parasites was at once manifest-the coarsely granular protoplasm and large nucleus with its curiously vacuolated nucleolus of the parasite contrasting strongly with the almost homogeneous protoplasm and compact intensely-staining nucleolus of tbe ovum. a ' Nature,' vol. xliii. p. 343. 3 Zool. Anz. xiv. 1891, p- 70. |