NATURE 



241 



THURSDAY, JULY 12, 1900. 



i 



A MONOGRAPH ON LAND-PLANARIANS. 

 Monographic der Turbellarien. II. Tricladida Terricola 

 {Landplanarien). By Prof. Ludvvig von Graff. Pp. 

 i + 574, and an atlas of 58 plates. (Leipzig : W. 

 Engelmann, 1899.) 



THE Turbellaria are rapidly becoming one of the 

 most adequately and conveniently described groups 

 of Invertebrates. Practically all that is at present known 

 as to their anatomy, classification and distribution is 

 comprised in three works — the " Monograph," by Prof, 

 von Graff ; the special memoir, by the same author, on 

 the " AcoL'la " ; and the masterly work, by Prof. Arnold 

 Lang, on the " Polycladida" in the series of monographs 

 on the fauna and flora of Naples Bay. The work before 

 us, a magnificent folio, completes the author's share in 

 the monographic treatment of the group. The first part 

 was published in 1882, and was reviewed in this journal 

 by Prof. Moseley. It is with great pleasure that we 

 notice the dedication of the second part — ^jointly to 

 Moseley and Fritz Miiller — as only one of the many 

 felicitous ways in which Prof, von Graff expresses his 

 admiration for the work of these his fellow-labourers in 

 the anatomy of planarians. We heartily congratulate 

 Prof, von Graff on the appearance of this volume, the 

 conclusion of a work begun twenty-five years ago. 



Apart from all other claims upon our notice, this 

 treatise is remarkable as being the first attempt to deal 

 exhaustively with an essentially tropical group of animals, 

 for nothing can be clearer, after reading this account, 

 than that land-planarians, though not restricted to the 

 tropics, have their headquarters in the equatorial forest 

 belt. Von Graff has himself spent some time in Java, 

 Singapore and Ceylon, and the personal acquaintance 

 made in this way with these animals, and the conditions 

 under which they live, gives a vividness and directness 

 to his descriptions. Other naturalists have notably 

 assisted him. Prof. Dendy, whose admirable and con- 

 tinued researches on the land-planarians of Australia and 

 New Zealand receive full acknowledgment in this work, 

 Spencer, Hamilton, Fletcher and others have sent collec- 

 tions of these animals to von Graff from Australia. 

 Striibell, Max Weber, the Sarasins and others have con- 

 tributed specimens collected by them in the Oriental 

 region. South America is represented by planarians 

 taken by Darwin, Fritz Miiller, von Jhering and Plate. 

 Nearly all the chief museums in Europe have contributed 

 their specimens to von Graff, and in this manner he has 

 been able, not only to more than double the number of 

 species which were recognised when he began this work, 

 but also to personally examine all but a very small per- 

 centage. To realise the rapidity of the increase in 

 species of land-planarians during the last twenty years, 

 it will be sufficient to state that Moseley's complete list, 

 made in 1877, comprised only 63 forms, while 125 were 

 known when von Graff began his monograph on the 

 group, during the course of which he has added no less 

 than 200 new species, and this, together with increments 

 from other sources, makes a total of 348. 



Of this unexpectedly large number (for it is about equal 

 NO. 1602, VOL. 62] 



to all the other Turbellaria put together which have been 

 really adequately described), less than a dozen occur 

 (with the exception of the Manchurian sub-region) in 

 both the Pahearctic and Nearctic regions. The majority 

 come from South America, the Oriental and Australian 

 regions. Even this statement, however, does not repre- 

 sent the richness of the tropics, for Australia is really 

 the only country where land-planarians have been 

 systematically collected and recorded. Our knowledge 

 of the planarian fauna of Africa, India, China, Central 

 and North America is almost a blank. And additions 

 to it will no doubt be made, not only in these countries, but 

 also in places in which naturalists have already sought 

 planarians. The island of Celebes, for example, has 

 been examined by several zoologists, who have searched 

 for land-planarians, but without success. Hickson, and 

 after him Max Weber, searched in vain. More recently, 

 however, the Sarasins have thoroughly explored the 

 island, and have brought to light a most interesting 

 fauna. Von Graff shows that the land-planarians of 

 North Celebes exhibit Oriental characters, those of 

 South Celebes Austro- Malayan features. Altogether 

 twenty-one Celebesian species are now known, and of 

 these all but three are new. We refer to this point par- 

 ticularly as showing that we are only beginning to realise 

 the variety of this element of the tropical fauna, and 

 that years of work are necessary in any one country 

 before the planarian fauna can be fairly estimated. In 

 Ireland a new species has been found near Dublin, and 

 two other additions to the land-planarians of Europe 

 have been made quite recently. 



The first part of von Graff's great work is devoted to 

 a full statement of the anatomy and histology of land- 

 planarians. This section must have involved a vast 

 expenditure of labour. Direct observation of the anatomy 

 of living or compressed specimens is impossible, owing 

 to the amount of opaque pigment in the tissues. Even 

 the external apertures are hard to discover. Dissection 

 is precluded by the solidity and tenuity of the body. 

 The only available means in the majority of cases is the 

 laborious one of serial sections, and this method the 

 author has applied to elucidate the structure of no less 

 than eighty-two species. 



The chief result obtained in this way is the uniformity 

 of the general anatomical features. Land-planarians 

 form a homogeneous group, and agree closely in structure 

 with the marine Triclad Turbellaria so far as these are at 

 present known. Their distinguishing features appear to 

 be correlated with the terrestrial habit. Among these 

 may be mentioned their greater size and more powerful 

 musculature ; the formation of a " keel " to the foot, and 

 the abundance of glands both for lubricating the foot 

 and for enveloping prey ; their brilliant, often intensely 

 brilliant, colouring ; the presence of sensory thickenings 

 and of sensory pits on the anterior part of the body ; 

 and, perhaps their most significant distinction, the pre- 

 sence of elaborate structures accessory to reproduction. 

 The anatomy of some of the simpler land-planarians is, 

 however, an almost exact repetition of an aquatic Triclad, 

 and the retention of cilia in the epidermis points to the 

 conclusion that in land-planarians we have the first 

 stage in the evolution of a terrestrial group from an 

 aquatic one. 



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