DEVELOPMENT OF LIMULUS POLYPHEMUS. 



201 



earlier stages of embryonic mammalia with the fishes and reptiles is to some minds very 

 significant, while to others differently constituted it is of little importance. 



To give completeness to this article T might cite Professor Huxley's latest expression of 

 his views as to the affinities of the Xiphosura. Dohrn quotes him as saying in the 

 "Academy" (Nov. 13, 1869, p. 42) "I imagine that the Copepoda represent the hypothetical 

 Archseocarida most closely. Apus and Sapphirina indicate the relations of these Archse- 

 ocarida with the Trilobita, and the Eurypterida connect the Trilobita and the Copepoda 

 with the Xiphosura. But the Xiphosura have such close morphological relations with the 

 Arachnida, and especially with the oldest known Arachnidan, Scorpio, that I cannot doubt 

 the existence of a genetic connection between the two groups." 



Finally Prof E. Van Beneden (on the Systematic Position of the King Crabs and Trilo- 

 bites, Annals and Mag. Nat. Hist., Jan., 1872, copied from Comptes Eendus de la Soc. 

 Entom. Belg., Oct. 14, 1871) after referring to Strauss-Durckheim's opinion that the Gna- 

 thopoda (Limulus) should form a separate order of the class Ai'achnida, remarks as 

 follows : "The Limuli are not Crustacea ; they have nothing in common with the Phyllo- 

 poda ; and their embryonic development presents the greatest analogy with that of the 



Scorpions and other Arachnida, from which they cannot be separated The 



Trilobites, as well as the Eurypterida and the Poecilopoda, must be sep- 

 arated from the class Crustacea, and form, with the Scorpionida and the 

 other Arachnida, a distinct branch, the origin of which has still to be 

 ascertained." 



Still later than Prof. Van Beneden's paper appears (as reported in "Na- 

 ture" for Jan. 17, 25, 1872) a paper " On the Anatomy of Limulus Poly- 

 phemus" by Prof. R. Owen, in which he adopts the view held by Prof. 

 Dana, that the telson of Limulus represents tlie abdomen ; hence "the vei'y 

 fact of the late appearance of tliis terminal division was decisive against 

 any real representative resemblance of the embryo Limulus to the Trilo- 

 bites." He also believes that there is "neither a nauplius stage nor a 

 trilobite stage" in the embiyo of Limulus ; though he considers Limulus a 

 Crustacean. 



On a deformed caudal spine of Limulus. The accompanying figure 

 represents, reduced one-half, a spine of a specimen of L. Polyphemus 

 which I found in company with Dr. E. Cones, at Fort Macon, North Caro- 

 lina. The specimen was twice the size represented by the cut, and was 

 bifurcate at the extremity in the manner shown by the figure. I am 

 inclined to believe that this deformity is very rare. 



Fig. 36. 



MKMOIKS BOBT. 800. KAT. HIST. TOL. II 



