ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 41 



pits ; these parabranchial stigmata are found on the posterior face of 

 the median sternal lobe which unites the two halves of the lamel- 

 ligerous appendage ; they are connected with powerful muscles, the 

 function of which is clearly to agitate the plate-like organ, for the 

 purposes of respiration. A still more intimate knowledge of the struc- 

 ture of the lamelligerous appendages in the two forms reveals their 

 essential similarity in structure ; an axis springing from the body- 

 wall has its posterior face provided with a transverse series of lamellae ; 

 when these are all set in a corresponding position we find that they 

 are always imbricated, and that the imbrication is identical in all, and 

 that they only present such diiferences, as density of structure, &c., as 

 are to be explained by a reference to their different positions and 

 functions. The history of these structures is next hypothetically 

 detailed, and it is pointed out that in living Scorpions the original 

 stigma has closed up and that a new opening (the stigmatic slit) has 

 been developed within the area formed by the closure of the stigma ; 

 and air now enters where before there was blood. 



The characters of the free entosternite in the two forms are then 

 described and compared ; and it is stated that in no Crustacean are 

 such developments to be observed. The alimentary tract is similarly 

 treated, and the fact that the proctodoeum is so short in Limulus is 

 stated to be one of the most important points of difference ; but this 

 itself is only a part " of that general reduction of its hinder seg- 

 ments " ; another difference is the absence of Malpighian glands in 

 the King-crab. This portion of the paper concludes with an account 

 of the circulatory and generative organs. 



The Eurypterina present numerous well-marked indications of 

 forming a link between the tw^o forms here compared together. After 

 a review of the opinions held by preceding writers, Professor Lankester 

 proceeds to the development in time of Limulus and the Tracheate 

 Arthropoda; from the latter he would separate the Arachnida as 

 not having any special connection with the Hexapoda and Myria- 

 poda, the exact relations of which to the other Arthropods is still a 

 matter for speculation. The Arachnida may be divided into three 

 orders: Hsematobranchia (= Merostomata), Aerobranchia (Scorpions 

 and Spiders), and Lipobranchia (Mites, Pseudoscorpions, &c.). 



Function of the Caudal Spine of Limulus.* — J. de Bellesme, 

 after pointing out that this organ cannot, on account of the mode of 

 disposition of the spinules on its lower surface, act as an organ of 

 offence, the need of which, for such a creature, can hardly be ima- 

 gined, states that the appendage may move vertically through 80% 

 and that it has a great power of lateral movement. When a King- 

 crab falls on its back, it flexes its prothorax and the tip of the spine 

 touches the ground ; the creature now rests on only two points ; easily 

 enough it sways to one side or the other till one edge of the carapace 

 touches the ground ; all that it then has to do is to alter its centre of 

 gravity by moving its limbs, and it will be found to veritably fall on 

 its feet. 



* Ann. Sci. Nat. (ZooL), xi. (1881) art. No. 7, 5 pp. 



