86 



epidermis — and not as in the Leech in a single layer of small co- 

 lumnar cells. 



2) Epidermic gland- cells. These were first described and 

 figured by L e y d i g , — but as Leuckart has remarked, their great 

 abundance and the very deep position which they may occupy, was 

 not insisted upon by him. They are seen in transverse sections as 

 transparent globular "bodies with nucleus and either clear or granular 

 contents — often in close proximity to the wall of the alimentary 

 cavity — whilst their narrow ducts reach forward in a radial direction to 

 open between the epidermic cells on the body-surface. The salivary 

 glands are aggregations of closely similar cells each with its own fine 

 duct — and their identity with the unicellular glands of the body- sur- 

 face is correlated with the fact that the pharynx is an invagination of 

 the ectoderm (stomodaeum) . 



Leuckart appears to me to have made a mistake in confusing 

 the true unicellular glands of the epidermis which sink so deeply into 

 the body — with certain deep-yellow granular cells which form a well 

 marked layer nearly surrounding the alimentary canal. The epidermic 

 gland-cells are pale and translucent and quite distinct from the yellow 

 or brown botryoidal tissue which Leuckart identifies with them. 

 This brown tissue as Leuckart rightly states is what Brandt indi- 

 cated as liver, whilst Ley dig considers it to be a kind of fatty body like 

 the fatty body of Insects (Leuckart, Menschl. Par. Vol. L p. 641). 

 Whilst the brown perienteric tissue or botryoidal tissue is quite distinct 

 from the epidermic glands — its true nature has been overlooked by 

 all previous observers, as will be shewn directly. 



It must be distinctly understood that we are able to confirm 

 Leuckart 's distinction of the epidermic unicellular glands into those 

 which are more superficial and those which sink deeply into the body 

 so as to abutt upon the wall of the alimentary canal. But the brown 

 botryoidal tissue (»Zellen von gelblichem Aussehen und gewöhnlich zu 

 unregelmäßigen Strängen und Trauben an einander gereiht« Leuckart) 

 has nothing to do with them. 



Connective tissue. The connective tissues of the Leech in- 

 clude three chief varieties which run into one another and further are 

 not to be sharply distinguished from the tissue forming the wall of the 

 smaller blood-vessels. The most massive tracts of connective tissue are 

 formed by a slightly fibrillated but otherwise homogeneous ground- 

 substance in which are very numerous oblong corpuscles with exceed- 

 ingly fine processes. The younger of these corpuscles are finely gra- 

 nular, the older contain abundant coarse straw-coloured granules of 

 larger size and high refractive index. Silver staining gives the appea- 



