178 



COMPARATIVE ANATOMY. 



walls (c) ; this, after a simple course, passes to tlie body-wall (e '), 



wliere it finds its opening. 



In the Chtetopoda simple forms of looped canals are most 



common, the separate canals in them 

 forming sometimes coiled bodies, 

 and sometimes presenting a very 

 few coils. The funnel-like internal 

 opening, which has been recognised 

 in many, has in some (Alciopa) just 

 the same relations to the septa of 

 the coelom as it has in the Scoleina. 

 In many of them the relation to the 

 generative system can be similarly 

 recognised. 



In addition to the more secon- 

 dary relations which the looped 

 canals of the Annelides have to the 

 generative system, either at certain 

 points only, or for a greater dis- 

 tance, their relation to the excre- 

 tion, as well as to the introduction or 

 expulsion, of water must be borne in 

 mind. That these organs have a close 

 relation to the function of excretion 

 is shovf n by the glandular investment 

 of their walls, and the glands which 

 open directly into them. They, in 

 fact, resemble the chief trunks of the 

 excretory organs of the Trematoda. 

 A relation between the perienteric 

 fluid and the surrounding medium, 

 either by the outflow of the former, 

 or the entrance of the latter, is 

 rendered possible by the internal 

 opening of the looped canal. From 

 the direction of the ciliary move- 

 ment in the canals, and at their 

 internal orifices, which is in nearly 



all cases towards the exterior, it is probable that sohds also may 



be moved in this dii^ection. Further investigation^ however, is 



necessary in order to confirm this supposition. 



Fig. 84. A looped caual of Luin- 

 bricus — not too highly magnified. 

 a Internal opening. hhb Clear 

 portion of the canal, arranged in two 

 double loops, c c Narrower portion 

 with glandular walls, d Widened 

 portion, which becomes narrower at 

 d', and at d" is continued into the 

 muscular portion, e. e' External 

 opening. 



Generative Organs. 



§ 146. 



We meet with a larger number of intermediate steps in the 

 sexual differentiation of the Vermes than in that of any other 

 division. The lowest stages are hermaphrodite, but this arrange- 



