CONTRIBUTIONS TO THE ANATOMY OP THE HIRUDINEA. 44 1 



Nephelis among the Gnathobdellidse have only a slight 

 amount of this tissue and are perfectly firm and rigid, almost 

 brittle to the touch while living. Hsemopis and Aulostoma 

 present the other extreme in this respect, and by no amount of 

 muscular contraction can they render themselves other than 

 " limp/^ while Hirudo, Trocheta, and Pontobdella 

 present an intermediate condition : usually fairly limp, by mus- 

 cular contraction they can make themselves rigid. The matrix 

 or ground substance, which, like all other intercellular substance, 

 presents a deep staining after treatment with nitrate of silver, 

 is perfectly hyaline and jelly-like. I have made no very 

 definite observations as to the development of this matrix but 

 there can be but little doubt that it arises by ectoplastic modi- 

 fication of the corpuscles lying within it. In the youngest 

 Pontobdella I have examined (recently hatched) the cor- 

 puscles (fig. 29.) in which are already undergoing various 

 metamorphoses, and are closely packed, there is as yet but 

 little matrix present. 



The corpuscles, originally doubtless rounded or but slightly 

 irregular in form, either remain in this condition, undergoing 

 a series of modifications (entoplastic metamorphoses) 

 while preserving their form ; or they may become elongated, 

 and it may be branched, giving rise to fibres, or giving rise to 

 pigment. They may undergo another series of modifications, 

 ectoplastic and entoplastic metamorphoses taking place simul- 

 taneously, resulting on the one hand in the pigmented patches 

 of the skin, on the other hand in vaso-fibrous and botryoidal 

 tissues. There is probably a fourth line of modification of these 

 primitive cells as the result of which they form capillaries. These 

 are only to be regarded as various lines of modification which 

 may take place simultaneously and to a certain extent overlap 

 one another. They will be best treated separately with refer- 

 ence to the whole group rather than simply described as they 

 occur in individual genera. 



1. Entoplastic metamorphosis — the cell preserving a rounded 

 form. Vacuolated-cells. Fat cells. 



The least modified cells are found in Pontobdella and 



