132 PATTEN AND REDENBAUGH. [Vol. XVI. 



only five pairs of these canals entering the pericardial sinus, 

 although Milne-Edwards describes six. 



From the pericardial sinus the blood enters the heart through 

 eight pairs of functional ostia. 



6. The Excretory System. 



The nephridia, brick-red glands, or coxal glands (PI. VII, 

 Fig. 2, n.^^), as they have been variously called, consist of a mass 

 of tubules in the cephalothorax on each side of the endocranium. 

 An elongated portion lies on the haemal side of the plastro- 

 coxal muscles, and four lobes {n.^~^) descend from this into 

 the bases of the second, third, fourth, and fifth appendages, 

 respectively. The lobes lie between the slips of the superior 

 plastro-coxal muscles and communicate with each other by 

 ducts on the neural sides of these muscles. A duct leads 

 to the exterior from the lobe in the fifth appendage. The 

 external opening {n.o^ is upon the posterior side of the base 

 of the fifth appendage. 



7. The Reproductive System. 



Limulus is dioecious, and the male can be distinguished by 

 the thicker and subchelate character of the second pair of 

 appendages which are used, during the breeding season, in 

 clinging to the posterior margin of the abdominal carapace 

 of the female. Both the ovary and testes are retiform, the 

 network of tubules, which compose these glands, extending 

 through the cephalothorax and a large part of the abdomen. 

 The paired oviducts and vasa deferentia have muscular walls, 

 and open to the exterior by apertures at the summits of two 

 genital papillae upon the posterior surface of the base of the 

 operculum. 



II. THE NERVOUS SYSTEM. 



As has already been said, we are indebted for out" kno.wledge 

 of the nervous system of Limulus chiefly to Owen and Milne- 

 Edwards, although Packard, Viallanes, and Patten have more 



