446 ALFRED CxIBBS BOURNE. 



years being completely digested by an Aulostoma in as many 

 days. The process of tissue-growth is more rapid in this than 

 in any other genus. 



In the connective tissue in the central region of the body 

 there are numerous rounded corpuscles which appear to be, 

 on the one hand, elongating, forming branched corpuscles^ and 

 on the other, to be developing pigment, arranging themselves 

 in rows. A metamorphosis of a portion of their substance 

 forms channels, which afterwards come into communication with 

 other similar channels and with the closed vascular system on the 

 one hand, and with the sinus system on the other, forming 

 *^botryoidal tissue." These processes are shown in fig. 28. 



The question as to whether the metamorphosis is ectoplastic 

 or endoplastic is one to which I shall revert below. 



The structure of the botryoidal tissue has been fully described 

 and figured by Professor Lankester for Hirudo in his pre- 

 viously cited memoir, where also will be found an account of 

 the previous observations upon the subject. Its vascular 

 nature was first recognised by Gratiolet in 1862 (loc. cit.). 

 Botryoidal tissue presents fairly similar characters in Aulos- 

 toma, Psemopis, and Hirudo. 



In Nephelis and Trochetait becomes specially developed 

 (fig. 63), In both genera it is exceedingly abundant and very 

 elastic, being capable of most extensive distension by blood as 

 also it is indeed in the other genera. Its special development 

 consists in its hollowing out to give rise to the remarkable 

 series of vascular dilatations which occur in these two forms — 

 the relations of which I have dealt with below in connection 

 with the vascular system (figs. 63 and 51). These diverticula 

 lodge the nephridial funnels. 



Nephelis presents the simpler arrangement, the portions of 

 the cells bounding the lumen remaining very irregular, the 

 lumen communicating freely at all points with the lumen of 

 the botryoidal tissue in the neighbourhood. 



In Trocheta this arrangement is somewhat modified. 

 Actually bounding the lumen is a single layer of pigmented cells 

 regularly arranged. The inner surfaces are slightly irregular 



