242 



NA TURt 



[July 12, 1900 



The presence of three extreme forms of rod-like 

 secretions and the absence of nematocysts are note- 

 worthy features of the epidermal glands. " Flame-cells " 

 and parts of the canalicular system of excretory vessels 

 have been found. The nervous system exhibits an 

 interesting series of modifications. In the most primitive 

 members of the gioup— the broad, flattened neotropical 

 Geoplanidte — the central nervous system consists of 

 a dense plexus forming a horizontal plate lying just above 

 the ventral body-wall. From this plexus nerves are given 

 off, which either at once enter some organ or join with 

 their fellows to form a well-developed cutaneous nerve- 

 plexus right round the body. There is no distinct 

 "brain." In the narrower neotropical and Australian 

 members of the same family, a concentration of this 

 central plexus takes place along two admedian lines, and 

 a marked anterior thickening indicates the "brain." In 

 the other families, as the sense-organs, which are scattered 

 in the GeoplanidiE, become massed in front, so does the 

 individuality of the brain become more and more pro- 

 nounced. These sense-organs are of four kinds. The 

 tentacles with eyes at their bases, found only in two 

 South American forms. A paired sensory ridge forming 

 a margin to the anterior part of the ventral surface in 

 Geoplanidye, and to the dorsal and ventral edges of the 

 "cephalic plate" of Bipaliida;. These ridges are inner- 

 vated by the cutaneous nerve-plexus. Then the sensory 

 pits which accompany these ridges, but which are sup- 

 plied direct from the central nervous system. Lastly, 

 the eyes. Of these there are two kinds. One, with the 

 usual Turbellarian type of structure, has the rods directed 

 away from the light, and the nerve entering in front and 

 not, as in most other Invertebrates, from behind. This 

 kind of eye occurs not only down both sides of the 

 whole length of the body in the Geoplanidae, but also on 

 the dorsal and even the ventral surface. In the Bipaliidas 

 such eyes are concentrated at the margin and angles of 

 the " cephalic plate." The other type of eye is one 

 common to most Invertebrates, but hitherto unknown in 

 Turbellaria. It consists of a pigment cap with a nerve 

 perforating it behind, and entering the rod-cells, which 

 face outwards towards the light. Such are the large 

 paired eyes of the Rhynchodemidae, and they are often 

 imbedded in the nervous matter of the " brain." 



The most novel and richly illustrated section of the 

 anatomical part of von GrafTs volume is, however, that 

 in which the unexpected complexity and variety of the 

 reproductive organs is discussed. This chapter is a 

 most important addition to Turbellarian anatomy, and 

 the results well repay the labour which has been spent 

 on its preparation and illustration. 



The next section, a short one, is devoted to the habits 

 of land-planarians. Here, as in the other sections, the 

 author has collected and given in extenso all the essen- 

 tially important information that has been previously 

 obtained. In this section, however, he adds little to the 

 observations of Darwin, Moseley, Dendy, von Kennel 

 and others. Land-planarians, though capable of with- 

 standing considerable variations of temperature, are 

 almost instantly killed by contact with dry objects, and 

 by immersion in water, whether fresh or salt. The 

 majority flourish best in dark, moist places. They 

 are nocturnal, living by day under stones and tree- 

 NO. 1602, VOL. 62] 



trunks, under the sheaths of bananas, and on tree-ferns 

 Some are actually subterranean, and live on earth-worms. 

 These are blind. But most land-planarians are content 

 with a diet of snails, woodlice and insects. Rhynchodemus 

 vejdowskyi is one of the few diurnal forms. It not 

 only crawls about by daylight, but moves with such grace 

 and rapidity that when von Graff saw it at Buitenzorg he 

 mistook it at first for a Myriapod. A species of Geoplana 

 has been found in some numbers creeping on the pave- 

 ment of Melbourne in broad daylight. 



The coloured plates, which show the appearance and 

 bizarre markings of land-planarians, form quite a feature 

 of von GraflPs work. The ground colour is usually 

 diversified by mottling or by brilliant longitudinal stripes. 

 Bold transverse bars of colour are comparatively rare, 

 but they occur in a small group of each of the two 

 families, Bipaliidas and Geoplanidae. It is an extremely 

 curious fact that all the barred species of the former 

 family are confined to the islands of the Malay Archi- 

 pelago ; all those of the latter to the (Chilian sub-region, 

 with a single exception found in Brazil. 



With reference to any supposed significance of these 

 colours, von Graff suspends his opinion. Dendy, it is 

 true, has shown that Geoplana produces an unpleasant 

 taste on the tongue, and that fowls readily pecked at this 

 planarian, but would not swallow it. A casual experi- 

 ment of this kind is, however, not sufficient to justify the 

 assertion that the colours of the land-planarians are of 

 the "warning" category. The great difficulty is how to 

 explain the prevalence of such brilliant colours and 

 definite patterns in a group which is almost exclusively 

 nocturnal. Yellow is the commonest colour, then orange, 

 red, green, blue and violet. In young specimens, the 

 pattern is more sharply defined, and the pigment (which 

 is present both in large, richly branched connective-tissue 

 cells and in the parenchymatous matrix) relatively more 

 abundant than in the adult. No experiments appear to 

 have been made to test whether land-planarians possess 

 the power of colour-change. As with many other groups 

 of animals upon which elaborate anatomical monographs 

 have been written, the physiology of land-planarians is 

 practically unknown. 



The distribution of this group is very interesting, and 

 is clearly illustrated by von Graff both by tables of every 

 species and by a coloured map. To one of the main 

 facts, their rarity north of the Equator and their abun- 

 dance m the tropics, I have already adverted. Another 

 interesting and suggestive discovery is the large pro- 

 portion which occur on islands. More than half of the 

 known species (201 out of 348) are purely insular, and each 

 of almost all these (186) is liinited to one island. As show- 

 ing that this is only one of several indications of the local 

 distribution of many species, von Graff points out that 

 only five land-planarians occur in two geographical regions, 

 only twenty in two subdivisions of the six regions, and 

 but eighteen in two parts of the same region separated by 

 an arm of the sea. The land-planarians afford a striking 

 proof of the value of the Sclater-Wallace regions, which 

 accordingly are adopted by the author. 



The Oriental region is, perhaps, the richest, certainly 

 the best characterised. Five-sixths of the family Bipa- 

 liidae are confined to this region, and the remainder occur 

 in Madagascar (most of the species being peculiar to this 



