THE COPEPODA 99 



and posterior sides by a chitinous wall. It seems not unlikely 

 that further research will show the wall to be formed by an 

 invagination of the cuticle, in which case it may represent the 

 vestige of a corneal pouch like that of the Branchiopoda. 



Reproductive System. The ovary (Fig. 55, B, ovy) is unpaired 

 and, at its first appearance in the larva, asymmetrically placed, 

 afterwards assuming a median position. Rudiments of two ovi- 

 ducts are found in the larva, but that situated on the same side 

 of the body as the ovary atrophies, while the other develops 

 further and ultimately opens (od) in the middle line between the 

 bases of the last pair of legs. 



A pair of spermathecae (Fig. 55, B, sp) are found in the 

 abdomen. They are not connected with the oviducal opening, but 

 each has a short duct which gives off a blind diverticulum and 

 terminates on a papilla with a retractile spiniform tip close to 

 the anterior margin of the abdomen. It is believed that the 

 sharp points of these papillae pierce the envelopes of the eggs 

 when the latter are laid, so as to permit the entrance of the 

 spermatozoa. The eggs are laid attached to stones or other objects. 



The testes (Fig. 55, C, /) are paired and lie in the abdomen. 

 Their ducts unite to form an unpaired seminal vesicle (s.v), and 

 after receiving the ducts of a pair of accessory glands (gl) lying 

 in the thoracic region again unite to open by a median pore (0) 

 between the bases of the last pair of legs. The seminal pouches 

 on the penultimate legs of the male and the structures connected 

 therewith have already been mentioned. 



DEVELOPMENT OF BRANCHIURA. 



In some species of Argulus the newly hatched larva has all the 

 appendages similar to those of the adult with the exception of the 

 first maxillipeds, which are not modified into suckers but are stout 

 clasping limbs, each consisting of four segments and ending in a 

 double claw. In other species, however, among which is the 

 common European A. foliaceus, the newly hatched larva differs still 

 more from the adult (Fig. 56). The antennae are biramous, having 

 a large unsegmented exopodite which is lost in the adult, and the 

 mandibles have a large uniramous palp of two segments. The 

 antennal exopodite and the mandibular palp are tipped with plumose 

 setae and serve as swimming-organs. The heart is not found in 

 the earliest larvae but develops after the first moult. 



REMARKS ON HABITS, ETC. 



The majority of the Eucopepoda are marine, but numerous 

 species, belonging chiefly to the families Centropagidae, Harpac- 



