TYPES OF SPECIES OF CKSTODA — KKKFFT. 25 



transverse fibres, these forming the boundary between the cortex 

 and the medulla (PI. iw. tig. 5). The inmost transverse muscu- 

 lature is the weakest of the three. The longitudinal bundles are 

 considerably elongated in the dorso-ventral direction. The inner 

 bundles each possess from thirty to forty fibres, whilst the outer 

 have about twenty. The differentiation into inner and outer 

 series is still recognisable laterally though the bundles become 

 much weaker. Dorso-ventral fibres are relatively powerful 

 though not numerous. Scattered throughout the cortex are 

 rounded calcareous corpuscles having a diameter of from O007 to 

 0015 mm. 



Nervous System. — The nervous system is seen to consist in 

 each segment of three pairs of relatively large, longitudinal 

 strands situated in the lateral region. The main nerve lies 

 dorso-laterally to the ventral excretory vessel, the dorsal and 

 ventral accessory nerves lying dorso-laterally, and ventro-laterally 

 respectively from the main nerve. The strands all lie well within 

 the inmost transverse muscular layer. The dorsal accessory and 

 the. main nerve pass dorsally over the cirrus sac, the other 

 nerve lying ventrally to it. 



Excretory System. — This system consists of the usual two 

 pair of vessels, the ventral pair being much larger than the 

 dorsal. The dorsal trunks possess a lumen of O026 mm., and 

 lie median wards from and just dorsally to the ventral vessel. 

 The surrounding parenchymals very rich in nuclei. The ventral 

 pair have a diameter of about O085 mm. Both vessels are dis- 

 placed dorsally in the region of the genital duct, the latter 

 passing ventraliy to them. A noteworthy point is the presence 

 in the posterior region of each segment of two transverse 

 excretory vessels, a narrow tube connecting the dorsal vessels 

 and a wide tube lying immediately below it and connecting the 

 two ventral vessels. This feature has already been mentioned 

 by Fuhrmann as occurring in Acoleus vag'inatus. The ventral 

 trunks were readily traceable into the scolex (see PI. iv., rig. 1). 

 Each became somewhat sinuous and eventually reached the level 

 of the anterior margin of the suckers as a wide vessel which bent 

 round to pass backwards for a short distance, and then trans- 

 versely behind the retracted rostellum to meet its fellow from 

 the opposite side. Probably the course is different when the 

 rostellum is everted. A narrow commissure connecting the limbs 

 of the loop was detected near the level of the mid-region of the 

 suckers. The dorsal vessels were not traceable into the scolex. 



