98 LABORATORY STUDIES IN ZOOLOGY 



of sensory appendages render services which are tactile and 

 chemical in nature. Note the openings of the nephridia (green 

 glands) on the middle of the ventral surface of the basal segment 

 of the antenna?. 



The cervical groove, already referred to, crosses the dorsum 

 of the carapace at about the middle of its extent and is thence 

 continued forward on either side as a groove, which ends just 

 laterad of the antennae. The cervical groove marks the boundary 

 between head and thorax. The ventro-lateral edge of the 

 carapace is not attached, the free plate on each side being known 

 as the gill cover, since underneath are found the gills by means of 

 which these animals obtain oxygen. 



When the animal is viewed from the dorsum, those appendages 

 constituting the mouth parts (serving as jaws and conveyors of 

 food to the mouth) may be seen projecting slightly beyond the 

 cephalic margin of the carapace. These appendages named in 

 order from the first or cephalic pairs are: mandibles, one pair; 

 maxillae, two pairs; maxillipeds, three pairs. Caudad of these 

 and borne by the thorax are five pairs of walking legs the anterior 

 pair of which is modified into large pincers termed chela. 

 The basal piece of the third pair of walking legs bears the genital 

 opening in the female. The fifth pair of walking legs in a 

 corresponding location bears the opening of the male genital 

 organs. The appendages will be studied in more detail later. 



The abdomen comprises seven segments six of which bear 

 appendages. These appendages are called swimmerets. In the 

 female they serve as attachments for the eggs which are thus 

 carried during the developmental period. The first pair of 

 abdominal appendages in the female are reduced. In the male 

 they are fused to form an organ for the transfer of sperm to the 

 female. In the sixth pair of swimmerets, called the uropods 

 (meaning "tail-foot"), the parts are greatly enlarged and form 

 with the telson (last segment bearing the anus) an efficient swim- 

 ming organ, termed the caudal fin. 



y On the appropriate plate label all the above-described struc- 

 tures, which are visible from the dorsal side. 



The Gills. — Remove the carapace of the left side and note the 

 pinnate (feather-like) gills underneath. Study those above 

 the second or third walkingjeg. The gill exposed at the base 

 of the appendage is the podohranch (foot gill). In the lobster 

 the delicate lamina uniting with its base and forming the division 



