842 SUMMARY OF CURRENT RESEARCHES RELATING TO 



a con-esponding condensation in this region. Behind the twenty 

 somites, whicli can be readily distinguished, there are indications of 

 several others. 



The epidermic cells themselves are not as in Peripatus, ever pig- 

 mented, biat pigmented connective tissue cells and vascular capillaries 

 may intrude upon them ; and the extent to which tliis takes place 

 varies in species, and even in individuals, and is the cause of the 

 coloured pattern which is seen on the surface of the body. Some of 

 the e2:)idermic cells may become glandular, and those are either 

 permanently dermic in position, when they are mucous in function, or 

 they may become " deep " glands ; the latter are salivary, clitellar, or 

 peristomial. Other epidermal cells may become sensory, but these 

 have already been fully described by Ley dig. The muscles were 

 found to be formed of elongated cells, which are either arranged in 

 bundles or set singly ; the cells may be much branched, and consist of 

 a cortical and medullary substance, greatly differentiated from one 

 anothei-. 



The histology and metamorphoses of the connective substance have 

 been carefully worked out. In the Ehyncobdellida3 the blood is 

 colourless, and there are very large numbers of colourless amceboid 

 corpuscles ; in the Gnathobdellidae the blood-ijlasma contains dis- 

 solved haemoglobin. There are two systems of blood-spaces, which 

 are, however, in communication with one another ; one represents the 

 closed vascular system, and the other coelom, vessels, and sinuses. 

 The coelom would appear to be a schizocoele, and this persists to some 

 extent in all the genera ; most fully develojied in the Ehyncobdellidae 

 it is reduced in Nephelis and Trocheta to the ventral sinus and its 

 immediate branches. In some a process has been taking place, which 

 it is proposed to speak of as a diacoelosis or scattering of the coelom — 

 connective tissue growths having more or less completely filled it up, 

 the remnants forming the sinus system. Different remnants remain in 

 different genera ; and the same organ may remain in each ; this is 

 perhaps best seen in the varying position of the nephridial funnel in 

 Clepsine, Pontohdella, and Hirudo. 



New coelomic spaces (botryoidal tissue) may be developed, and 

 such a process is spoken of as pseudoccelosis ; the proof of this new 

 space being " ccelomic " is given by its inclosing the nephridial 

 funnel, as in Neplielis. The process may be explained as due to an 

 archaic enterocu3le having gradually undergone diacoelosis and been 

 replaced by a pseudoccele. " This primary and secondary coelom exist 

 simultaneously side by side in all existing Gnathobdellidae. In the 

 Rhyncobdellidse considerably more of the primary coelom remains, and 

 the secondary coelom has not yet appeared upon the scene." 



In conclusion, attention is directed to the nephridia, all of which 

 (even those of Hirudo) have coelomic orifices ; the funnels are found to 

 present a serial modification from the fairly developed condition seen 

 in Clepsine to the many lobed, ciliated, spongy mass which is found in 

 Hirudo. The degenerate condition of the portion of the gland which 

 follows on the funnel is probably to be explained by its function 

 having been taken on by the blood-vessels. 



