LESSON 35.] NUTRITION IN THE CIKRIPEDIA. 123 



these animals, straight, and terminates by a vent, at the extremity 

 opposite to the head. The intestine is fusiform, and divided by a 

 series of slight constrictions into sacculi (minute sacs, d). 



It is maintained in its position by a transverse muscle (h) ; the 

 walls of the abdomen are distinctively provided with longitudinal 

 (i) and transverse (k) fasciculi of muscular fibres. 



567. The nervous system consists of a single cephalic ganglion, 

 placed on the ventral surface, from which are continued two princi- 

 pal chords (^, g) extending along the under surface of the body. 

 The heart may be seen in the middle line of the cephalo- thorax 

 (head, chest), propelling the blood forwards. Two canals pass 

 from it into the hollow feet ; the rest of the blood is distributed to 

 the head, and along each side of the commencement of the alimen- 

 tary canal to the under part of the body, where it passes backwards 

 in the vessel which accompanies the intestine. 



568. The ovaria (o, o) at first appear as long, blind tubes, sac- 

 culated along the outer side. As the ova become developed, the 



ovarium takes on the form of a bunch of grapes, 



, . ,, . , ., , , FIG. 205. 



and occupies the whole cavity of the abdomen ex- 

 ternal to the intestine ; each ovarium terminates 

 by a triangular, and somewhat prominent orifice, 

 to which the external ovisac (f) is appended. 

 This latter structure agrees with the form of ex- 

 ternal ovisac in the lower Crustacea, into which 

 the ova pass from the abdominal cavity (having 

 attained a certain degree of maturity) through the 

 oviduct e, for their full development, previous to 

 the fertilizing influence of the male. 



569. The disparity of size in the sexes is considerable, as appears 

 by the annexed figure of the Male Actheres (Fig. 205). 



LESSON XXXY. 



ORGANS OF NUTRITION IN CIKEIPEDIA. 



570. Like the Epizoa, many of these animals are parasitic, but 

 unlike the latter, these have only a residence on the bodies of ani- 

 mals, obtaining their food from oilier sources : thus the Tubicinella 

 is parasitic in the skin of the Whale, but it does not obtain its suste- 

 nance, or any portion thereof, from the animal whose skin it inhabits. 



