896 SUMMARY OF CURRENT RESEARCHES RELATING TO 



favour of their having had a common ancestor with the Triclada, but 

 whether the Leeches have advanced or the Triclads degenerated is a 

 problem that has yet to be solved. 



External Morphology of the Leech.* — C. 0. Whitman, as all 

 who have worked at the species of Hirudinea will allow, justly refers 

 in strong terms to the superficial and slovenly manner in which the 

 diagnoses of species have been drawn up. He points out that no one 

 appears to have suspected the existence of segmental sense-organs in 

 the leech, and much less their serial homology with eyes. In the 

 present essay he attempts, further, to show that the rings and somites 

 form the only proper basis of classification. 



The segmental sense-organs are in the form of papillae, of which 

 there are twenty-six transverse rows — one for each somite ; they are, 

 also, so disposed as to form eight longitudinal rows — two median, four 

 lateral, and two marginal ; the first may be regarded as the metameric 

 equivalents of the first pair of eyes. While the true eye consists of 

 a cylindrical mass of cells, three or four times as long as wide, in 

 which the central portion is made up of peculiar large glassy cells, 

 with a vacuolar central space, probably filled with some kind of fluid, 

 the sections of the segmental papillae present all the same elements, 

 with the exception of a pigment-cup. The originals of the papillse 

 may have represented sense-organs of a more or less indifferent 

 character, of which a few at the anterior have become light-perceiving 

 organs, while the rest have either remained indifferent, or become 

 specialized in another direction. Suggestions are made as to the 

 relations of these organs to the segmental sense-organs of the lateral 

 line in fishes. 



A comparative study of Hirudo and the genera allied thereto is 

 next entered on, and a careful definition of the genus Hirudo is given. 

 The investigation of the abbreviated somites shows that abbreviation 

 is greatest at either end of the body ; the first six somites have lost 

 seventeen rings, the last four eleven ; this abbreviation is not, how- 

 ever, an actual loss, it is only a sacrifice in the interest of the rings 

 retained ; at the anterior end there has been a higher development of 

 the sense-organs, at the posterior a greater development of muscles. 

 It is very interesting to note that it is the non-papillate rings that 

 have been suppressed ; the abbreviation is believed to be still going 

 on, and not to be equally rapid in different genera. 



The author gives a table indicating his views as to the relation- 

 ship of the genera, and in a postscript refers to Mr. Bourne's recent 

 work, in which, he points out, there is no discussion as to the nature 

 of the segmental papillae, and in which the number of somites is 

 determined by that of the ganglia. 



Action of a Secretion obtained from the Medicinal Leech on the 

 Coagulation of the Blood.t — Prof. J. B. Haycraft describes a series 

 of experiments on the action which a secretion, obtained by solution 

 from the medicinal leech, has on the coagulation of the blood, as 



* Proc. Amer. Acad. Sci., xx. (1884) pp. 76-87 (1 pL). 

 t Proc. Eoy. Soc, xxxvi. (1884) pp. 478-87. 



