CONTRIBUTIONS TO THE ANATOMY OF THE HIEUDINEA. 443 



2. Ectoplastic metamorphosis. The connective-tissue cells 

 of most widespread occurrence are the elongated or branched 

 corpuscles described and figured by Professor Lankester from 

 Hirudo where they are easily studied. They may be even 

 more easily seen in Haemopis^ but best of all in Pontobdella 

 (fig. 2o, a, b, and fig. 9, c). They occur in all the genera 

 throughout the group. 



In young Clepsine and Pontobdella I have seen them 

 as quite short, stout cells (fig. 29). They doubtless develop 

 from the indifferent corpuscle above mentioned. As they 

 enlarge they become packed with large, highly-refringent, 

 regularly-arranged globules. These never run together, as 

 do the fat-globules described above. Although they become 

 blackened by osmic acid they are not dissolved by the ordinary 

 fat solvents ; they are not, therefore, fat. 



The cells present two, three, or four processes, which become 

 immensely elongated and attenuated ; so much so that fre- 

 quently the body of the cell is hardly recognisable. It is these 

 processes and in the Hirudinea these aloue, which form the 

 fibres which run in all directions in the connective jelly. 



In Pontobdella I have observed that these fibres may 

 become perfectly elastic in character, appearing twisted and 

 coiled in a teazed preparation (fig. 30). 



The nuclei of these cells remain small, but I have fre- 

 quently noticed them undergoing division in Pontobdella 

 (fig. 25, a). 



I cannot pretend to say, in the present state of our know- 

 ledge of comparative histology, how far this mode of origin of 

 the fibres from cells in the Hirudinea bears upon the mode of 

 origin of the fibres of areolar connective tissue in Mammalia. 

 It shows, at any rate, the possibility of their developing by the 

 mere elongation and branching of cells. 



3. Ect-entoplastic metamorphosis. The cell developes 

 pigment. 



a. The cells take no part in the formation of a vascular 

 system. This series of modifications is best seen in Pontob- 

 della and the other Rhyncobdellidee. Whether it occurs at 



