CONNECTIVE AND VASIFACTIVE TISSUES OP LEECH. 307 
On the Connective and Vasifactive Tissues of the Me- 
dicinal Leech.^ By E. Ray Lankester, M.A., F.R.S., 
Professor of Zoology and Comparative Anatomy in 
University College, London. With Plates XXVII and 
XXVIII. 
The minute comparative anatomy of that group of tissues 
which is more or less vaguely indicated by the term con- 
nective substance (with which I should associate — as is not 
usually and expressly done — the vasifactive [angioplastic] 
derivatives of connective tissue^) has yet to be worked out, 
and when the task has been accomplished the great con- 
nective-tissue question/’ in which histologists were but lately 
so keenly interested, will be settled. 
There can be no doubt that from the point of view of 
general morphology, as well as from the more special point 
of view of the histologist, the proper understanding of the 
nature and relations of the varieties of connective and vasi- 
factive tissue is of fundamental importance. You have in 
the ideal connective substance an element the vast possi- 
bilities of which first impressed the mind of Bichat — an 
element which can assume the widest variety of form and 
function, embracing the conditions known as tendon, fat, 
capillaries, cartilage, areolar tissue, and endothelium. 
To study the origins of this tissue and its varieties in 
lower forms of organisation cannot but be a fruitful labour, 
since the histological differentiation of the higher Vertebrates, 
no less than their grosser morphological composition, must 
be traced, if we are rightly to comprehend it, to simpler and 
more archaic phases which are to some extent at least pre- 
served in those branches of the great animal pedigree which 
have not advanced so far from a primitive ancestral condition 
as have the Vertebrata. 
Ectoplastic and entoplastic tissues . — The most fundamental 
distinction which can be drawn morphologically between the 
various kinds of connective tissues, is one which also serves 
to divide other groups of tissues and depends on the mode 
‘ See also ‘ Zoologisclier Auzeiger,’ 1880, No. 49. 
’ The term “ connective tissue ” is used very unfortuuately in differing 
degrees of comprehensiveness — sometimes cartilage, sometimes fat, and 
sometimes bone, being excluded or included as the case may be. I would 
propose the term “ skeleio-trophic ” fora natural group of tissues which is 
divisible into — (1) Skeletal, including fibrous, adenoid, adipose, bony, and 
cartilaginous tissues. (2) Vasifactive, including capillaries and embryonic 
blood-vessels. (3) Hjemolymph, including the hanna or hccmaglobiuous 
clement and lymph, the colourless element of vascular fluids. 
