THE CRUSTACEA 



base. These glands appear to be a specialisation of some of the 

 dermal glands which (as in many Eucopepoda) are abundantly dis- 

 tributed over the surface of the body. 



Alimentary System. The alimentary canal has a narrow oeso- 

 phageal region, with strong circular and longitudinal muscles, which 

 projects, funnel-like, into the wide stomach. The latter gives off 

 a pair of diverticula, which are much ramified, and occupy the 

 greater part of the lateral lobes of the cephalothorax. When feed- 

 ing, these diverticula, as well as the stomach and intestine, become 

 filled with the juices of the host. The stomach is followed by a 

 wide intestinal region which is separated by a sphincter from the 

 narrow rectum. The latter is without the dilator muscles found 

 not only in Eucopepoda but in most Crustacea. 



Circulatory System. The heart is situated at the junction of 

 thorax and abdomen, and sends off an aorta which reaches as far 

 forward as the brain. It is provided with one or two pairs of 

 lateral and inferior afferent ostia and sometimes a median inferior 

 efferent opening at the base of the aorta. There appears to be 

 doubt as to the existence of a posterior median efferent opening. 

 In the earliest larval stages the heart is absent, and the circulation 

 is mainly carried on, as in the later stages it is assisted, by 

 rhythmical contractions of dorso-ventral muscles in the abdomen. 



Excretory System.- An excretory gland of the usual type is 

 present, and has been identified as the maxillary gland (shell- 

 gland). It appears from the investigations of Glaus and of 

 Nettovich, however, that it differs from the maxillary gland of 

 the Eucopepoda and other Crustacea in opening not on the maxilla 

 but on the first thoracic limb (the so-called " second maxilliped "), 

 o'r on the sternal surface of the body close to the base of that 

 appendage. 



Nervous System. The ventral nerve-chain (Fig. 55, A) is 

 shortened, but six ganglia can be distinguished. The statements as 

 to the origin of the nerves to the two pairs of maxillipeds are con- 

 flicting, but the last four ganglia supply the somites of the four- 

 pairs of swimming-feet, the last also sending nerves to the abdomen. 



Sense-Organs. A median (nauplius) eye of the usual structure 

 is set upon the dorsal surface of the brain (Fig. 55, A, e). In 

 addition, there are a pair of large compound eyes (Fig. 54, e) 

 visible through the transparent integument of the dorsal surface. 

 Each is supplied by a stout optic nerve which swells into a 

 ganglion before entering the eye. The eye is movable, but it 

 differs from the similarly movable, non-pedunculated eyes of the 

 Branchiopoda in the fact that it moves not in a "corneal pouch" 

 but in a blood-space which intervenes between the outer ends of 

 the quadripartite crystalline bodies and the integument. Seen 

 from above this blood-sinus is bounded on the anterior, external, 



