298 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 39. 



fibrous band in which a pair of giant fibers are visible. The nuclei 

 are practically confined to these ganglia, and even in them they 

 diminish greatly in number from in front backward, so that in the 

 sixth segment it is often impossible to distinguish them. After divid- 

 ing in the sixth segment the rami run alongside the intestine, giving 

 off branches to the trunk muscles. Toward the posterior end of the 

 abdomen each ramus divides into a dorsal branch going to the anus 

 and a ventral one going to the anal lamina. In each segment of the 

 thorax a pair of nerves is given oft' to the trunk muscles in addition 

 to those going to the swimming legs. 



The eye. — The eye of Ergasilus is situated far forward in the frontal 

 region and in immediate contact with the ventral surface (fig. 15). 

 It consists of three hemispherical ocelli, two lateral and one infero- 

 median, im.bedded in sockets lined with pigment. Each ocellus is 

 composed of a number of rounded fusiform cells, arranged radially 

 and containing a nucleus near their outer end. The central mass is 

 divided by two partitions, one superomedian, separating the lateral 

 ocelli, the other infero-horizontal, separating the lateral ocelli from 

 the inferior one. The latter looks directly downward on the ventral 

 surface, which bulges slightly outward at this point and probably 

 serves as a cornea. The lateral ocelli also face downward and only 

 slightly outward, and no separate corneal facets for them can be 

 detected. 



Summary. — 1. The entire nervous system, including both ganglia, 

 the ring around the gullet, the cord, and the eye, is exclusively ventral 

 in position and lies close to the ventral surface. 



2. Both the prse and the postesophageal ganglia are enormously 

 elongated, so that together they extend the entire length of the 

 stomach. 



3. The ring around the gullet contains cellular as well as fibrous 

 elements, and is therefore a cord rather than a commissure. 



4. The nerves supplying the second antennae originate from the 

 anterior end of the prseesophageal ganglion. 



5. The ventral cord is really a pair of cords lying side by side and 

 connected by a fibrous band with two giant fibers. 



6. Both ganglia are perforated in the vicinity of the gullet by mus- 

 cles extending to the mouth-parts. 



REPRODUCTIVE ORGANS. 



In the female the reproductive organs consist of a paired ovary, 

 convoluted oviducts, and a pair of shell glands; the oviducts lead 

 backward on either side to the vulva, which opens on the dorsal sur- 

 face of the genital segment, while the shell glands extend forward 

 from the genital segment into the free thorax (fig. 21). 



