ZOOLOGY. 433 



9. It agrees with Scorpio iu possessing vibratile spermatozoa. No 

 Crustacea, except Cinhipedia, are knowntoliave vibratile spermatozoa. 



10. It agrees with Scorpio aud Spiders in having a brain which (like 

 that of that embryo Scorpion and Spider) supplies only eyes and integ- 

 ument with nerves, and not any appendage. In all Crustacea, except 

 some Phyllopoda, such an archicerebrnm does not exist; but even in 

 young stages the brain is found to supply at least one pair of append- 

 ages, as well as the eyes. 



11. It agrees with Scorpio in the concentration of the origins of 

 nerves supplying the anterior part of the abdomen, in the cephalothorax, 

 in the form of a nervous collar, perforated by the pharynx. Such a 

 nerve-collar has its parallel in Crustacea, among the brachyurous Deca- 

 poda, which, however, are in other respects the Crustaceans which least 

 resemble Limulus. 



The points in which Limulus agrees with the Crustacea and differs 

 from Arachnida are three only. They are as follows: 



1. Limulus agrees with many Crustacea, and differs from Arachnida, 

 in that its respiratory organs are adapted to an aquatic in place of an 

 aerial medium. 



2. Limulus agrees with Crustacea, and differs from Arachnida, in that 

 it possesses a pair of groups of eyes, in which the association of the 

 individual eyes of each group is so close as to constitute a compound 

 eye. 



3. Limulus agrees with Crustacea (excepting some Isopoda?), and 

 differs from Arachnida, in not possessing glandular coeca (the Malpi- 

 ghian tubules) growing out from the proctodteum. 



Li conclusion, Professor Lankester referred the Merostomes unreserv- 

 edly to the class of Arachnids, and divided that class into three sub- 

 classes, or "grades," the first of which he calls Haematobranchia — a 

 new name for the Merostomes — and the other two of which are desig- 

 nated Aerobrauchia (Scorpionina, Pedipalpi, and Araneina) and Lipo- 

 branchia (Solifugaj, Pseudoscorpionina, Opilionina, and Acarina). 

 Among the Haematobranchia he recognizes three " orders," viz : — Trilo- 

 bita, Eurypterina, and Xiphosura. 



Legs of Trilohites. 



The Trilobites have long been favorite objects for the collector of fos- 

 sils, occur iu exuberant abundance in many rocks, are very often found 

 in fine condition — so far at least as the dorsal portion is concerned — 

 and have been the subjects of several thoughtful monographs. Never- 

 theless, Piofessor Huxley, in 1877, gave expression to the current belief 

 respecting them when he wrote (Amit. Invert. An., p. 258) that ''up to 

 [that] time, no certain indications of the existence of appendages, nor 

 even of any hard sternal body-wall, [had] been discovered, though ii 

 shield-shaped labrum, which lies in front of the moutb, has been pre- 

 served in some specimens." But iu that same year, 1877, Mr. C. D. 

 S. ]Mis. 101) 28 



