1871.] WOODWAED XTPHOSURA. 57 



the youtliful Sao hirsuta and Trinucleus ornatus ; indeed, he might 

 well add, with the young of Agnosias, Aidacophura, Phacops, Hy- 

 drocepJudus, and with every other Trilobite with whose young stages 

 the illustrious Barrande has made us acquainted. 



He also notices the remarkable analogy which the nearly mature 

 embryo presents to Belinurus and Preshvichia — a resemblance 

 which I pointed out in my paper (already referred to and read be- 

 fore the Society in November 1866), 



Dr. Dohrn refers to Prof, Huxley's memoir on Pterygotus (pub- 

 lished in the Memoirs of the Geological Survey, Monograph I., on 

 the Eurypterida, 1859) to show that at that time Prof, Pluxley 

 saw no possibility of combining the Eurypterida with the Xi- 

 phosura. But, considering the materials within Prof. Huxley's 

 reach, as compared with those which it has been my good fortune 

 to have the advantage of studying, it is hardly fair to condemn the 

 classification of the later writer upon the opinion of a high zoolo- 

 gical authority (like that of Prof. Huxley) published nine years be- 

 fore that in which the monograph on the Merostomata appeared, 



I have long been aware that Prof. Huxley has concurred in my 

 classification of this group, and in his latest published " Synopsis of 

 the Animal Kingdom " (in Jukes's ' Manual of Geology,' dated 1872), 

 he has adopted the order Merostomata for ''■ Eing-crabs, Eury- 

 pterus, tEC." 



Prof. Hiickel believes the Trilobites to be a suborder of the 

 Phyllopoda, from which perhaps the Poecilopoda descended. He 

 again divides the PcEcilopoda into two legions, viz, the Xiphosura 

 and Gigantostraca *. 



In this view Gegenbaur agrees with Hackel. 



I will now quote the final paragraph from Dr. Dohrn's paper, 

 and then give my reasons for dissenting from his conclusions. 



" The more the theory of evolution is allowed a direct influence 

 in zoological work, the more conspicuous is its preeminently prac- 

 tical character, inasmuch as it not only solves problems, but also 

 suggests a correct method of inquiry. Thus, it is true, it destroys 

 the traditional system ; but it sets up a new one immediately : and 

 thus, if we ask for the result of its application as made in the pre- 

 sent memoir, we arrive at the folio wing conclusions : — 



" Limulus is most nearly related to the Gigantostraca ; both seem 

 to be related to the Trilobites, although it is not possible to demon- 

 strate all the details of their relationship. 



" The morphologico-genealogical relations of these three families 

 to the Crustacea cannot at present be established, and perhaps may 

 always remain doubtful. 



" It is also impossible at present to say any thing definite con- 

 cerning the relationship between them and the Arachnida. 



" Therefore all we can do is to combine these three families under 

 a common name, for which I would propose Hackel's expression 

 Gigantostraca, and to place them in the system beside the Crustacea." 



* See his 'Generelle Morphologie.' The Gigantostraca being Tterygotus, 

 Eiirypterus, &c. 



