32 PLATYIIELMINTHES TURBELLARIA CHAP. 



sea-level in England, the Isle of Man, and Ireland, and from its 

 abundance in spring water, probably enjoys a wide distribution 

 underground. In the Swiss Alps it has been found at altitudes 

 of over 6000 feet, at lower levels in the Khone, and also in the 

 Lake of Geneva. This wide distribution may perhaps be accounted 

 for, partly, by its faculty for asexual reproduction in summer, and 

 also, by the production, later in the year, of hard-shelled eggs which 

 are laid loosely, not attached to stones or plants. 1 But we have 

 no really direct evidence of the means of dispersal of this or of 

 any of the foregoing species, although they all have a wide 

 distribution in Europe. Of extra-European forms the accounts 

 that exist are very fragmentary. The only indubitable diagnostic 

 character of a Triclad is the structure of its genital ducts, and 

 this is accurately known in only a few cases. Several species 

 such as Dicotylus pulvinar (Fig. 16, B), at present known only 

 from Lake Baikal, 2 and others (Planaria mrazekii, P. albissima') 

 from Bohemia, 3 will doubtless be found elsewhere when they are 

 carefully looked for. Phagocata gracilis is a remarkable North 

 American form, possessing several pharynges (Fig. 14, C and C'), 

 recalling the independent movement of the pharyngeal lobes of 

 Discocelis lichenoides (Fig. 9). 4 



Occurrence of the Maricola. Little as we accurately know 

 of the distribution of the fresh-water Planariae, our knowledge 

 of the occurrence of the marine forms is still more limited. 

 Gunda (Procerodes) ulvae (Fig. 14, D) is the commonest European 

 form, occurring abundantly in the upper part of the littoral zone, 

 on the shores of the Baltic. G. segmentata from Messina has 

 been carefully described by Lang, 5 but these are almost the only 

 species of Maricola which can be accurately determined. They 

 differ from the Paludicola in the position of the " uterus " behind 

 the genital pore and in the absence of a " inusciilo -glandular 

 organ " (Fig. 1 4, F). A special interest attaches to the Bdellouridae, 

 a family containing three species, all parasitic on Limulus from the 

 east coast of America. These remarkable Triclads usually have a 

 sucker at the hinder end of the body, by which they attach 

 themselves firmly to the cephalo-thoracic appendages and to the 



Voigt, Zool. Am. xv. p. 238. 



Grube, Archivf. Naturgeschichte, 38 Jahrg. Bd. i. 1872, p. 273. 



Vejdovsky, Zeitschr. f. vvss. Zoologie, Bd. Ix. 1895, p. 200. 



Wood worth, Bulletin Mus. Comp. Zoology, Harvard, vol. xxi. No. 1, 1891. 



Mitth. Zool. Stat. Ncapcl, 1882, p. 187. 



