87 



ranee of colourless branched spaces on a dark -brown ground. The 

 second variety is one in which the ground- substance is thrown into the 

 form of ramifying fibres, the protoplasmic corpuscles being placed at 

 intervals on the 'fibre. These fibres are usually beset with fine brown- 

 coloured granules. They form an investment or tunica propria to 

 nearly all the more important organs — e. g. to the blood-sinus of the 

 nerve cord, to the lateral blood-vessels, to the nephridia (excretory 

 glands), and to the separate muscular bundles of the body wall. It is 

 to this variety that the pigment bodies of the integument belong. 

 There appears to be no sharp distinction between these 

 branching pigmented fibres and some of the blood- 

 vessels. Blood-vessels occur which are nothing more than such 

 fibres hollowed out. This is not surprising when we compare the facts 

 which have been ascertained as to the development of blood-vessels in 

 the omentum of the Rat. Nevertheless there are in the Leech abundant 

 minute blood-vessels which have exceedingly delicate walls devoid of 

 granules and a distended appearance and regular diameter — which 

 makes them resemble the finer blood-vessels of the Earthworm. The 

 third variety of connective tissue in the medicinal Leech might per- 

 haps be better described as a variety of blood-vessel — but as a matter 

 of fact the walls of blood-vessels are nothing more nor less than con- 

 nective tissue. This third variety is the brown botryoidal tissue sur- 

 rounding the alimentary canal. It consists of moniliform tubes which 

 are highly tortuous and branched, — the branches ultimately loosing 

 their moniliform character and becoming ordinary blood-vessels. 

 The cells which form these tubes are closely 'set around the lumen 

 which they enclose and are oval and of great relative thickness ; their 

 protoplasm is entirely obscured by an abundance of dark yellow or 

 brownish granules. The granules stain deeply with osmic acid, also 

 with goldchloride. 



The lumen of the tubes forming the botryoidal tissue 

 is occupied by the red blood of the Leech : the fat-body of 

 Leydig, the liver of Brandt; the epidermal glands of 

 Leuckart, is in reality a vascular plexus. This I have most 

 amply proved again and again both in fresh preparations and in trans- 

 verse sections. For the examination of the latter I can strongly recom- 

 mend the use of Ran vier 's Picrocarmine, as a colouring agent. The 

 vascular plexus of the botryoidal broAvn tissue must not be confounded 

 with that which occurs on the wall itself of the intestine. 



A vascular plexus adjoining the alimentary canal and having upon 

 its walls large cells highly charged with deep -yellow granules is 

 well-known to occur in the Chaetopodous worms and more especially 



