i'i'4 ZOOLOGY SECT. 



cavity of the pharynx opens in front into the intestine (int.), which 

 almost immediately divides into three narrow main branches, one 

 running forward in the middle line, the other two running back- 

 wards. Each of these three main branches gives off numerous 

 smaller branches, which in turn become branched, so that the 

 whole intestine forms a ramifying system, extending throughout 

 the greater part of the body ; all the branches terminate blindly, 

 an anal aperture being absent. 



A system of vessels the water-vessels or vessels of the excre- 

 tory $i/*fciti(ex.) sends ramifications through all parts of the body. 

 There are two main, considerably coiled, longitudinal trunks, right 

 and left, which open externally on the dorsal surface by means of 

 several minute pores ; in front they are connected together by a 

 transverse vessel. Each main trunk gives origin to a number of 

 branches, which in turn give off a system of extremely fine capillary 

 vessels, many of which terminate in flame-cells (Fig. 203, p. 253). 

 A flame-cell is a nucleated cell having in its protoplasm a small 

 space, into which one of the capillaries leads; in this space lies a 

 bundle of vibratile cilia, or a single thick cilium, which performs 

 regular undulating movements, giving it somewhat the appearance 

 of a flickering candle-flame. Cilia also occur in the course of 

 some of the capillaries. This system of vessels is usually regarded 

 as excretory; but it may also have a respiratory function. 



A well-developed nervous system (Fig. 172) is present. At 

 the anterior end is a central knot of nerve-matter, the brain (br), 

 from which proceed backwards two longitudinal nerve-cords (I. ne.}. 

 The brain consists partly of transverse fibres connecting to- 

 gether the two longitudinal nerve-cords, partly of groups of nerve- 

 cells situated at the ends, or in the course of, the nerve-fibres. 

 The nerve-cords give off both internally and externally numerous 

 transverse branches, which divide into finer twigs ; the internal 

 branches of the two cords frequently anastomose, thus forming 

 commissures or connecting nerve-strands between the two. A 

 number of nerves extend forwards to the anterior margin, which 

 is highly sensitive. 



Reproductive System. The reproductive organs (Fig. 173) 

 are hermaphrodite or moncecious in their arrangement, both male 

 and female organs occurring in the same individual. The genital 

 aperture leads into a small chamber, the genital cloaca, which 

 is common to both the male and the female reproductive 

 systems. 



The male part of the apparatus consists of tcstes, rasa deferentia, 

 and cirrus ov penis. The testes (tes.) are numerous rounded glands, 

 situated near the right and left borders. Two ducts, the right 

 and left vasa dcferentia (v. d.\ run backwards from the neighbourhood 

 of the te^tes and unite in the middle line posteriorly. The median 

 duct formed by the union of the two vasa deferentia traverses a 



