360 PALAEOSTEACA. 



A striking feature in some of the forms (Eurypterida) in this group is the scale- 

 like marking of the body-plates. 



A homology is naturally suggested, and has been carried out by RAY 

 LANKKSTER, between the coxal glands of the Arachnida and Xiphosura and a 

 pair of Crustacean nephridia. This could only apply to the shell-gland, which 

 belongs to the segment of the second maxillae, i.e. to the fifth limb-bearing 

 segment. We should then have to homologise the chelicerae of the Arachnida 

 with the first pair of antennae of the Crustacea, an assumption which seems to 

 us somewhat daring, and not sufficiently supported by the structure and 

 development of the brain in the two groups. There is the less need for a 

 homology between the shell-gland of the Crustacea and the coxal gland of 

 Limulus and Scorpio, as we have to imagine each body-segment originally 

 provided with a pair of glands of this kind, an assumption which appears to be 

 justified by a comparison with Peripatus.* 



LITERATURE. 

 I. Trilobita. 



1. BARRANDE, J. Systeme Silurien dn Centre de la Boheme. 



Prague et Paris. Premiere Partie. Tom. i. 1852. And 

 Supplement Tom. i. 1872. 



2. FORD, S. W. On some Embryonic Forms of Trilobites from 



the Primordial Rocks at Troy, N. Y. Amer. Journ. Sci. (3). 

 Vol. xiii, 1877. 



3. FORD, S. W. On additional Embryonic Forms of Trilobites 



from the Primordial Rocks of Troy, K". Y., etc. Amer. 

 Journ. Sci. (3). Vol. xxii. 1881. 



4. MATTHEW, G. F. Sur le developpement des premiers Trilobites. 



Ami. Sac. Roy. Malacologicjue de Belgique. Tom. xxiii. 1888. 



5. WALCOTT, C. D. The Trilobite: New and Old Evidence relating 



to its Organisation. Bull. MILS. Gump. Zool. Harvard Coll. 

 Cambridge. Vol. viii. 1880-1881. 



6. WALCOTT, C. D. Fossils of the Utica Slate. Trans. Albany 



Inst. Vol. X. 1879 (?). Contains statements as to the 

 metamorphosis of Triarthrus Becki. 



7. ZITTEL, K. A. Handbuch der Palaontologie. Bd. i. Abtheil. ii. 



Miinclten and Leipzig, 1885. 



[* The new discoveries of the antennae and limbs of a Trilobite (Triarthrus} 

 have advanced our knowledge of these fossils and of their affinities so greatly, 

 that the student must not rest content with the foregoing. The recent observa- 

 tions of BEECHETiand BERNARD (App. to Lit. on Trilobita, Nos. I., II., III., IV.) 

 have taken the point off many of the author's comments on the valuable infor- 

 mation given above. The text is translated as it stood on account of the matter 

 it contains, and the reader is merely referred to the more recent works on 

 the subject. This seems to be the only alternative to re-writing the whole 

 chapter. ED.] 



