536 



NATURE 



[April 4, 1901 



over the lower third of the macula, with the exception of 

 the Asaphidas, Illasnus and Lichas, of which they remark 

 the entire macula shows " the structure which charac- 

 terises " it as a visual organ. Beyond this, the macula, 

 for which an average diameter of 0*99 mm. is given, is 

 described as " oblong or ellipsoidal, and for two-thirds of 

 its surface perfectly smooth or rather glossy," and its 

 "granules " or lenses are estimated to be but 0*055 i^i"- 

 in diameter at their largest. 



With the maculae, as with the cephalic eyes, a wide 

 range of modification is recognisable, which, if the authors' 

 assumption of a visual function for the former be correct, 

 leaves little doubt that the facetted type is for it a 

 culminating one. They state that the maculcC, " whether 

 they show any organic structure or not," have commonly 

 an " excessive thinness of their shell," and in so far as 

 they enter into comparison with other Crustacea, while 

 they call attention to the similarity " in the formation of 

 the superior surface of the head in the Trilobites and the 

 embryos and newly-.hatched larvae of Limulus," they 

 incline to the belief that, concerning the cephalic eyes, 

 Limulus " stands completely isolated amongst all Arthro- 

 pods," except for a certain resemblance between its 

 cornea and that of Peltura." They similarly deny 

 reseniblance to the Phyllopods, and regard " the eyes of 

 the Trilobites " as showing " the greatest conformity 

 with those of the recent Isopods." 



Full perusal of the details which they attribute to the 

 hypostomial macula shows them to have discovered an 

 interesting and important organ. Comparison is instituted 

 between it and a thin area of the hypostome of the living 

 Apus ; but, if sound, there is not much to be said from 

 this standpoint for the "eye" theory in any but the 

 facetted forms. For the types which remain, the study 

 of the remarkable details described in the memoir leaves 

 us in doubt as to the evidence for the supposed visual 

 function. Convinced of its actuality, however, in an 

 attempt to bring the living Crustacea into line, the 

 authors fall back upon the fact that in the embryo 

 Limulus the median eyes have been described by 

 Packard and others as originally ventral, and that there 

 have been recorded for the Lepadidae two ventro-lateral 

 eyes in an adult by Darwin, two ventro-lateral and a 

 ventro-median one in a larva by Claparede, and similar 

 indications by Hesse and Spence Bate. 



Remarking upon the supposed habits of the Trilobites, 

 of which we know nothing very definite beyond that a 

 burrowing habit has been suggested, our authors express 

 themselves averse to the popular idea that they " lived 

 in abyssal depths . . . where the most intensive dark- 

 ness prevailed." There are, however, considerations 

 arising out of recent discovery concerning these animals 

 worthy of note in this association. Owing to the wonder- 

 ful conditions for preservation which characterise the 

 Utica slate deposits near Rome, N.Y., certain Trilobites, 

 during the last six to seven years there unearthed, as all 

 zoologists are well aware, in the hands of Dr. Beecher, 

 of Yale College, Conn., have yielded results of importance 

 second to none in the palaeontology of the period. The 

 proof that but one pair of antennae were alone present, 

 and that they were uniramous, brings the adult Triarthrus 

 at once into line with the Nauplius larva, as distinct from 

 all other known Crustacean forms ; while that of a simple 

 NO. 1640, VOL. 63] 



uniformly jointed condition of the post-oral appendages, 

 most, at least, of which were biramous, and of the Phyllo- 

 podan tendency of those posterior and last developed^ 

 more than fulfils the highest expectations of the philo- 

 sophic morphologist, and amply justifies our trust in the 

 larval form. One conspicuous feature of these appendages 

 is the recurrent development from each of an inwardly 

 directed and tapering gnathobase, most assuredly con- 

 cerned with its fellows in the seizure of the prey and, by 

 transfer of this from limb to limb, with its passage to the 

 mouth. We know nothing of the habits of these animals 

 as they swam, but from this feature the possibility is 

 suggested that, like the living Apus, they may have swum 

 upon their backs ; and, if so, the presence of hypostomial 

 eyes would beco.me the more readily intelligible. On the 

 other hand, the possibility that the " maculae " may have 

 been luminous organs must not be overlooked ; and 

 bearing upon this surmise, it is well to remember that 

 such organs are known to exist in a lenticulate and 

 aggregated form, and that the probable presence of one 

 of simple type in a sponge, taken in conjunction with 

 the extent to which like organs are functional as a lure 

 to the prey, would dispose of any anomaly in their 

 possession by blind animals. And finally, inasmuch as 

 the remarkable organs present in the Chitons, some of 

 which, being lens-bearing, were by Moseley described 

 as eyes, so far as experiment with light has yet pro- 

 gressed, have given but negative results, it becomes a 

 question whether, until we know more concerning even 

 these, the term "aesthete" may not be well extended to 

 them all. Arguing by analogy from these to the Trilobite 

 "maculae," it must be admitted that their visual function 

 is not proved. 



In the further inquiry into the nature of these remark- 

 able organs there lies a most promising field. As we 

 cannot experiment with them, we provisionally retain an 

 open mind concerning their functions ; and while we are 

 profoundly grateful to our authors for their intensely 

 interesting memoir and the great labour they have 

 bestowed upon it, we shall await with much interest the 

 further results of their inquiry. G. B. H. 



THE RELATIONS OF THE OSTRICH-LIKE 

 BIRDS. 

 On the Morphology and Phylogeny of the Palaeognathae 

 {Ratitae and Crypturi) and Neognathae {Carinatae). 

 By W. P. Pycraft. Trans. Zool. Soc. London, vol. xv. 

 pp. 149-290, pis. xlii-xlv. 



THE relation of the flightless ostrich-like birds (Mr. 

 Pycraft says we must no longer call them Ratitae) 

 to more typical representatives of the class Aves has 

 long been one of the puzzles of ornithology, and it is 

 therefore a matter for satisfaction that the author of this 

 important memoir has undertaken the task of revising 

 and extending our knowledge of the anatomy of the 

 existing members of the former group. The work was 

 undertaken in connection with Mr. Walter Rothschild's 

 revision of the cassowaries, of which, indeed, it forms 

 the sequel ; and the thorough manner in which it has 

 been carried out forms a model of what such researches 

 should be, and enables zoologists to draw their own 

 conclusions on the questions at issue, if they are unable 

 to accept all those at which the author arrives. 



I 



