NOTES ON THE DEVELOPMENT OF THE ARANEINA. 167 
Notes on the Development of the Araneina. By F. M. 
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 Aran- 
eina 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 de- 
velopment 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 
Claparede (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 pub- 
lished some very important observations on the development 
of the blastoderm. Finally, Barrois (No. 2) has quite re- 
cently 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- 
VOL. XX. NEW SER. M 
