ON THE DEVELOPMENT OF THE ARANEINA. BY F. M. BALFOUR, M.A., F.R.S., FELLOW OF TRINITY COLLEGE, CAMBRIDGE. Reprinted from the Quarterly Journal of Microscopical Science,' April, LONDON: PRINTED BY J. E. ADLARD, BARTHOLOMEW CLOSE. 1880. UNIV. OF NOTES on the DEVELOPMENT of the ARANEINA. By FM BALFOUR, M.A., F.R.S., Fellow of Trinity College, Cambridge. With Plates XIX, XX, and XXI. THE following observations do not profess to contain a complete history of the development even of a single species of spider. They are the result of investigations carried on at intervals during rather more than two years, on the ova of Angelena labyrinthica; and I should not have published them now, if I had any hope of being able to complete them before the appearance of the work I am in the course of publishing on Comparative Embryology. It appeared to me, however, desirable to publish in full such parts of my observations as are completed before the appearance of my treatise, since the account of the development of the Araneina is mainly founded upon them. My investigations on the germinal layers and organs have been chiefly conducted by means of sections. To prepare the embryos for sections, I employed the valuable method first made known by Bobretsky. I hardened the embryos in bichromate of potash, after placing them for a short time in nearly boiling water. They were stained as a whole with hematoxylin after the removal of the membranes, and embedded for cutting in coagulated albumen. The number of investigators who have studied the development of spiders is inconsiderable. A list of them is given at the end of the paper. The earliest writer on the subject is Herold (No. 4); he was followed after a very considerable interval of time by Claparède (No. 3), whose memoir is illustrated by a series of beautiful plates, and contains a very satisfactory account of the external features of development. Balbiani (No. 1) has gone with some detail into the history of the early stages; and Ludwig (No. 5) has published some very important observations on the development of the blastoderm. Finally, Barrois (No. 2) has quite recently taken up the study of the group, and has added some valuable observations on the development of the germinal layers. In addition to these papers on the true spiders, important investigations have been published by Metschnikoff on other groups of the Arachnida, notably the scorpion. Metschuikoff's observations on the formation of the ger |