ARTHROPODA 269 



of uterine processes in which the ova accumulate, and finally 

 opens on the posterior thoracic segment, which in the female is 

 fused with the first abdominal. Just at the point of opening 

 the oviducts receive the ducts of the spermatheca ; this is a 

 sac lying within the fused segments, and having a special 

 pore through which the spermatozoa . make their entrance 

 (Fig. 159). 



The testis resembles the ovary in form and position ; the 

 vasa deferentia are rather coiled, and may be divided into 

 different sections, they open into two vesiculae seminales, one 

 on each side of the sixth thoracic segment, and these open to 

 the exterior upon the same segment (Fig. 158). 



One fertilisation sufBces for many broods of ova ; the eggs 

 as they leave the oviduct are surrounded by a cement-substance 

 which forms an investment for each egg and keeps them 

 together in an oval mass, which the female carries one on each 

 side of her abdomen. One of the ovisacs may contain from 

 seventy to ninety ova. 



The Calanidae differ from the Cyclopidae in the possession 

 of a well-developed heart,, which in Calanella is produced into 

 a cephalic artery; and in the fact that their antennae are 

 biramous. The Notodelphidae which inhabit the branchial 

 chamber of Ascidians have their antennae modified for attach- 

 ment, and the posterior thoracic segments of the female are 

 fused together and form a brood -pouch in which the eggs 

 develope. 



(&) Parasitica. — The parasitic or semi-parasitic Copepods 

 have their mouth parts adapted for piercing and sucking ; their 

 body is usually incompletely segmented, and the abdomen is 

 reduced. The males are often smaller than the females to whom 

 they adhere. 



Most of the Parasitica live on fish, hence their common 

 name, fish-lice; they may inhabit the gill -chamber, or the 

 pharynx, or they may live on the skin, in which the female 

 buries half her body, and in some instances, e.g. Penella, they 

 even bore into the body and live partly embedded in the tissues. 



Chovdracanthus gihhosus, which inhabits in considerable 

 numbers the gill-chamber of the Lophius, or fishing-frog, exhibits 

 many of the peculiarities of these remarkable epizoa. The 



