G10 SUMMARY OF CURRENT RESEARCHES RELATING TO 



it considerable attention is given to a comparative study of the 

 different genera, with the object of finding a more satisfactory basis 

 for classification than any yet employed. All the Hirudinidffl agree in 

 having twenty-six somites between the first pair of eyes and the aceta- 

 bulum. There is a general law of abbreviation which is true of both ends 

 of the leech, and the extent of this, which consists in the suppression of 

 from one to four of the less important rings in the extreme somites, 

 not only furnishes excellent means for distinguishing genera and 

 species, but also gives a key to their phylogenetic relationship. The 

 land-leech {Hsemadipsd) is first considered. H. japonica is a new 

 species. The author points out that the land-leech, in abandoning the 

 aquatic mode of life, became more and more adapted for creeping till 

 at last the power of swimming was completely lost. This change in habit 

 was accompanied by adaptive changes in size, form, and proportions ; 

 the centre of gravity travelled backwards nearer to the posterior sucker, 

 while muscular power became more and more concentrated. The 

 nephridial vesicles are capacious sacs, and experiment shows that fluid 

 can be discharged from the nephridia for the purpose of moistening the 

 surface of the body. The skin-glands are more numerous and the 

 nephridial vesicles more capacious in terrestrial than in aquatic 

 leeches. Further, the nephridial pores are marginal, and not latero- 

 ventral in position, as are those of Hiruclo. In all land-leeches which 

 have been examined by I)r. Whitman, there have been noted the 

 absence of an eyeless ring between the two rings which bear the third 

 and fourth pairs of eyes ; the marginal position of the nephridial 

 pores ; the large size of the vesicles ; and the peculiar lobes which 

 cover the posterior pair of pores. All these characters appear to be 

 due to the change of respiratory medium, but the land-leeches still 

 req uire to live in air which is loaded with water ; they are animals 

 " still on the road to terrestrial life." Hirudo nipponia sp. n. is next 

 described, and the discussion of its characters leads the author to give a 

 revised definition of the genus Hirudo. With it he compares Aulostoma 

 and Hsemopis, the latter of which he proposes to replace in Hirudo, the 

 comparative number of denticles being of no importance in the defini- 

 tion of a generic group of the HirudinidaB. 



By a comparison of Hirudo medicinalis, Aulostoma, Hirudinaria 

 javanica and Leptosoma (g. n.), the author illustrates the value of the 

 somites as a basis for classification. This last-named form has fewer 

 abbreviated somites than the other forms described, and so shows that 

 it is more primitive than any known Hirudinid. The fact that the 

 denticles are rudimentary or absent suggests affinity to Aulostoma, but 

 the latter is clearly an offshoot of Hirudo, so the edentulous condition 

 must be supposed to have been acquired independently. L. pigrum, 

 L. edentulum, and L. acranulatum are the new species of this new 

 genus. The generic and specific characters of Dlacrobddla sestertia 

 are fully given. 



In conclusion Dr. Whitman speaks of the segmental papillae, 

 which, as he has already taught us, are serially homologous with the 

 eyes. They are sense-organs, and from them the eyes are developed, 

 so that they may be regarded as incipient eye-spots. These segmental 



