STRUCTURE OF NEPHRIDIA OF THE MEDICINAL LEECH. 283 
On the Structure of the Nephridia of the Medicinal 
Leech. By A. G. Bourne, Assistant in the Zoological 
Laboratory of University College, London. (With 
Plates XXIV and XXV.) 
The investigation into the structure of the so-called seg- 
mental organs, or (better) nephridia ’’ of the medicinal 
Leech, of which the following pages give an account, was 
undertaken at the suggestion of Professor Lankester and 
carried out under his direction and with his supervision and 
advice in the zoological laboratory of University College, 
London.^ 
A series of very successfully prepared sections of the 
Leech, made by Mr. J. E. Blomfield, of Oxford, at present 
Demonstrator in Prof. LankestePs laboratory, had sufficed 
to draw our attention to a number of interesting points in 
the minute structure of that animal. 
Amongst others. Professor Lankester especially pointed 
out the remarkable structure of the constituent cells of the 
nephridia, each cell being either perforated by a simple duct 
or having within its substance an arborescent extension of 
the system of ducts, common to the whole gland. Further, 
each cell was seen to be enclosed in a mesh of the capillary 
system filled with red fluid (the heemal system), which is 
spread throughout the tissues of the medicinal Leech. 
I undertook the more thorough investigation of these 
structures with two objects in view. In the first place, since 
the community of origin of the renal organ of Vertebrates, 
Worms, and Molluscs, has become a well-established theory, 
it cannot but be a matter of the first importance that the 
complete anatomy of the various modifications of the t) pical 
NEPHRiDiuM ” (as Professoi* Lankester^ has termed the 
single excretory tube from the multiplication or branching 
of which more complex forms, such as the primitive kid- 
ney or archi-NEPHRON, have been derived) should be care- 
fully worked out. 
In the second place, it is known that in Leeches this 
organ presents very wide differences of structure in different 
genera, difierences which appear to go hand in hand with 
corresponding modifications of the haemal system, and I was 
therefore anxious to obtain a complete knowledge of the 
^ See bis “ Observations on tlie Microscopic Anatomy of the Leech,” iu 
the ‘ Zoolog. Anzeiger,’ 1880, No. 49. 
^ “ Notes on Embryology and Classification,” this Journal, 1877. 
