394 ZOOLOGY 



corresponding with the second, third, fourth, and fifth prosomatic 

 limbs. In the adult this structure, which has been termed the 

 coxal ^/awc^, appears to have no duct, but in the young, both an 

 internal and an external opening have been described. The 

 former opens into a space in the connective tissue which lies 

 between the gland and the ventral blood sinus ; the external 

 opening is situated on the dorsal surface of the coxa of the fifth 

 appendage. The chitinous covering of the animal is continued 

 a short distance into the duct. The gland thus appears to 

 have the relationship of a nephridium, and it is worthy of note 

 that it opens upon the same appendage in numerical sequence 

 as does the shell-gland of the Entomostraca, the latter having 

 its orifice on the second maxillae, or fifth appendage. 



The nervous system of Limulus consists of a supra-oeso- 

 phageal nerve mass which gives off five nerves, supplying the 

 ocelli, the compound eyes, and the integument in the region of 

 the head (Fig. 223). From the sides of this mass pass a pair 

 of oesophageal commissures, which come together some dis- 

 tance behind the oesophagus ; the commissures are, however, 

 united together by a number of transverse connectives situated 

 behind the oesophagus. This elongated oval collar supplies 

 nerves to all the limb-like appendages, and to the operculum 

 which bears the genital orifices. After the fusion of the two 

 circum-oesophageal commissures, the nervous system is prolonged 

 backward as a ventral nerve cord, which during the first half 

 of its course gives off no nerves, but its posterior half supplies 

 five pairs of nerves, which pass to the last five appendages and 

 the surrounding parts. 



Both the oesophageal collar and the ventral nerve cord, and 

 many of the more important nerves, are ensheathed in blood- 

 vessels. 



Limulus is dioecious, and the male can be distinguished 

 from the female by the thicker and non-chelate character of the 

 second pair of appendages. Both the ovary and the testis are 

 retiform, the network of tubules which compose these glands 

 extending through the pro-, meso-, and meta-soma. The tubules 

 of the testes are in communication with a number of spherical 

 sperm vesicles, which contain immature spermatozoa ; the latter, 

 when ripe, are provided with a motile tail. Both the ovaries 



