-.Qog CRUSTACEA. 



are absent, and there are only four. In 108 and 111, a second inner 

 is wanting, and consequently there are but three setae. In 109, one 

 seta is very much elongated, so as to be much longer than the animal, 

 and the others are very short. 



The same variations take place with the setae of the lamellar stylets, 

 except that the number never exceeds five. This number is seen in 

 112. In 113, the inner of the five is wanting, and there are but four; 

 and in 114, the outer as well as inner is wanting, leaving but three. 



Circulatory system.— We have ascertained little regarding the circu- 

 lating system, except recognising in most species the existence of a 

 heart in the posterior half of the thorax. What we have on this sub- 

 ject will be presented in connexion with the descriptions of the genera 

 and species. 



Genital system.— -The seminal duct of the male extends from the 

 abdomen forward in the cephalothorax as far as the mouth, where 

 there is a pair of ovoid or pyriform glands which are united together 

 at the smaller apex. The ovarian ducts are much convoluted on 

 either side of the cephalothorax, and often extend quite to the front 

 of the animal. Figures will be referred to, and farther descriptions 

 beyond. 



Nervous system. — A large ganglion exists over the mouth and sur- 

 rounds the oesophagus, the latter passing upward from below through 

 it. In the species where it was studied, there was no other ganglion. 

 The nerves of the eyes, anterior antennae, and front portions of the 

 animal, were distinct; and the cords passing to the posterior members 

 start from this ganglion, and give off branches, without an enlargement 

 in any part (see figures 2 a, g, Plate 88) . In such species, therefore, the 

 nervous system fails of presenting the important characteristic distin- 

 guishing the Articulata from the Mollusca,— that is, a succession of 

 ganglia for the separate segments, although in its position and in 

 the external structure of the animal, the articulate character is very 



distinct. . 



Further details will be given on these points in connexion with the 

 description of particular species on the following pages. 



Classification.— Among the Cyclopoidea, we distinguish three families. 

 There are species in which the mandibles and maxillae have a jointed. 



