THE CLASSIFICATION OF CRUSTACEA 41 



female Cyclops carries her eggs until they hatch, in 

 two oval packets attached to the sides of the 

 body. 



Forming a separate order (BRANCHIURA) apart from 

 the more normal Copepoda (order EUCOPEPODA) is 

 the little group of the Carp-lice, one of which, 

 A rgulus foliaceus, is common in England, living as a 

 parasite on different species of fresh-water fish, and 

 often found swimming free in ponds and rivers It 

 has a broad, flat, and very transparent body, about 

 three-sixteenths of an inch in length. It differs 

 from Cyclops in a great many points, of which, 

 perhaps, the most conspicuous is the possession of a 

 pair of true compound eyes in addition to the 

 median eye. On the under-side of the head are a 

 pair of large round suckers, by means of which the 

 animal fixes itself on to its prey. A study of their 

 development shows that these suckers are really the 

 maxillae, which in the young animal are jointed 

 limbs ending in a strong claw, but later become 

 changed into the suckers of the adult. A sharp 

 spine, which can be protruded in front of the mouth, 

 is connected with what is believed to be a poison- 

 gland. The eggs are not carried in packets by the 

 female as in Cyclops, but are deposited on stones or 

 water-weeds. 



The fourth subclass, CIRRIPEDIA, comprises the 

 Barnacles and Acorn-shells. These are very unlike 

 any of the other Crustacea, and, in fact, they were 



