THE EPIZOA. 237 



terial gland, into which the spermatozoa pass on their way to 

 the oviducts. The gland thus plays the part of a sperma- 

 theca. The eggs are carried about in the ovisacs until they 

 are hatched. 



The vitellus undergoes complete division, and a morula 

 results, the blastomeres of which soon become differentiated 

 into a superficial epiblast, surrounding a deeper-colored mass, 

 which gives rise to the hypoblast and mesoblast. The whole 

 embryo then becomes divided by two constrictions into three 

 segments, and the hypoblast arises by delamination around 

 a central cavity, which becomes the alimentary canal. There 

 is a large labrum on the ventral side of the first segment in 

 front of the mouth. The eye appears on the tergal aspect of 

 the most anterior segment, as two pigment-spots which soon 

 coalesce into one ; and a pair of jointed setose limbs grows 

 out of each segment. In this JVauplius-staite the young Cy- 

 clops leaves the egg. 



The posterior part of the body elongates and becomes 

 divided into the somites of the thorax and abdomen, from 

 which their respective appendages bud out ; and these 

 changes are accompanied by exuviation of the cuticle. The 

 three pairs of appendages of the JVaitplius are converted into 

 the antennules, antennae, and mandibles of the adult. 



There are a few other fresh-water and many marine 

 genera of Copepoda. Among the latter, the Pontellidoe are 

 remarkable for the separation of that part of the head which 

 bears the antennules and the antennae, from the rest, a pecu- 

 liarity to which a parallel can be found only among the Sto- 

 matopoda. Corycoeus has two large, more or less lateral 

 eyes in addition to the median eye, subchelate antennae, and 

 a rudimentary abdomen. The beautifully iridescent Sapphi- 

 rina has an extremely depressed body, short filiform an- 

 tennae, two eyes, and rudimentary gnathites. A short tho- 

 racic heart is present in some genera. 



The Epizoa. — Insensibly connected by such genera as 

 jErgasilus and Caligus with the typical Copepods, are a great 

 number of very singular Crustacea^ which, from their habit 

 of living parasitically upon aquatic animals (whence their 

 vulgar name of "fish-lice"), have received the title of Epi- 

 zoa. Chondr acanthus gibbosus, commonly found in great 

 abundance on the walls of the branchial chamber of the 

 Fishing-frog [Lophius piscatorius), may serve very well as 



