Introduction to Animal Morphology. 



163 



Fig. 22. 



a semicircle of many eyes (Hemicyclia). 4. Dirhagea with 

 two grooves, which may be very long (Nemertes, Lineus), 

 or short, with four (Tetrastemma*), or no eyes (Meckeliaf). 

 5. Tetrarhagea with four grooves (which are converging 

 x-like (Ophiocephalus), or short, transverse (Loxorrhochma). 

 Schu!/zeand Mclntosh divide Nemerteans into two sub-orders : 

 i. Anopla with no style in the proboscis ; the nerve trunk 

 placed between the muscular 

 layers ; the mouth opening be- 

 tween the commissures ; deve- 

 lopment with metamorphosis. 

 This includes : i. Lineidae 

 with elongated ganglia ; the 

 body muscles externally longi- 

 tudinal, mesially circular, and 

 internally longitudinal ; the 

 proboscis has no internal, 

 longitudinal nor reticular layers, 

 but consists of five coats, ex- 

 ternal elastic, external longi- 

 tudinal, circular, basement, 

 and glandular laminae ; the vessels in the cesophageal wall 

 form a rete mirabile ; the head fissures are deep ; a separate 

 longitudinal band is detached from the investing stratum of 

 longitudinal fibres. Lineus has a long, slit-like mouth and 

 variable eyes ; Borlasia a slender proboscis ; Cerebratulus a 

 flattened body, thinning to the edge, and a cross-like arrange- 

 ment of fibres at each pole of the proboscis in transverse 

 Micrura and Meckelia are also included hen in. 

 inellidae with the lateral nerves between the base- 

 ment and the outer circular layers, and no head grooves nor 

 ' ; it includes (\arinella, with a short mouth 

 snout; and Yaleneinia, with a Ion:; mouth and 

 narrow snout. 3. CYphululhririihi- have a \\iile interval le- 



I and 111-- . nned with 



Diagram of Bipinnaria (p. 136) (R), and 

 a worm (C) ; A.c, anterior ciliary crown ; 

 m, mouth ; m, stomach ; P.c, posterior 

 ciliary crown ; a, anus. 



:nma lias i 

 .uarc. 

 t M le or no he. 



