56 PHYSIOLOGY OF THE INVERTEBRATA. 



digestive gland or pancreas. In Diaptomus orientalis, first 

 described by Dr. Brady,* the anterior portion of the intestine 

 is dilated ; but, speaking generally, the digestive system of 

 the Cojjqjoda is a simple tube devoid of appendages. 



(26) The RldzoccphaJa form the first order of the Pccto- 

 straca ; and they are parasitic organisms. The body is sac- 

 like, and, unlike the majoritj^ of the Crustacea, is devoid of 

 limbs and segmentation. The mouth is funnel-shaped, and 

 is surrounded by chitin. There is no alimentary canal. In 

 fact, we have in this order one of the reversions to a very 

 low type of digestion. 



(27) The Cirripcdia contain the barnacles {Lcpas) and the 

 acorn-shells {Bdanus). 



The mouth in Lcpas faces the posterior end of the body and 

 leads into a short oesophagus, which dilates into a stomach. 

 The stomach j^asses into the intestine, which is bent upon the 

 former organ. The intestine tapers gradually to the anus, 

 which is situated at the base of the caudal appendage. The 

 stomach is covered by small branched glands which are pan- 

 creatic in function. 



The food of the barnacles (consisting of small marine 

 animals) is brought to the mouth by the currents produced 

 by the cirri. In the words of Prof. Huxley, " a barnacle may 

 be said to be a crustacean fixed by its head, and kicking the 

 food into its mouth with its legs." 



The majority of the Cirripcdia are hermaphrodites, but in the 

 so-called supplemental or complemental male o{ ScaJpcUum nd- 

 gare (one of the Balanida' or sessile Cirrijx'dia^ there is neither 

 mouth nor alimentary canal. In ScaJpeJlum ornatum the com- 

 plemental males have no mouth ; but in Scalpcllum rostratum 

 thesi^ males have a well-developed alimentary canal. f 



(28) The Ampltipoda have a laterally compressed body with 

 branchife attached to the thoracic limbs. The mouth opens 

 into a straight and simple alimentary canal. The ducts of 



* JJinu Soc, Journ. Zovl., vol. 19, p. 296. 

 + Sje Darwin's Monn(jrojili of the Cirrijudia. 



