118 RAMBLES OP A NATURALIST. 



has long been regarded as characteristic of the type. 

 Here it is composed simply of two lateral ganglia, 

 from whence proceed two cords, which extend to the 

 extremity of the body, and give off merely very small 

 threads. Two large vessels, placed on either side, 

 accompany these nervous trunks, a third winds 

 along the median line ; all three are simple, without 

 ramifications of any kind. The mouth consists of a 

 circular orifice, which is scarcely visible, and opens 

 into a long tube, separated by a constriction from the 

 intestine, which terminates in a cul-de-sac. Thus 

 the same opening serves for the introduction of the 

 food, and for the rejection of the undigested residua. 

 As if to compensate for the low degree of develop- 

 ment in these organs, the ovaries, which are placed 

 on either side of the body, are of very considerable 

 dimensions. This very circumstance, however, is in 

 itself an indication of the inferiority of the animal. 

 These degraded species are besides exposed to a 

 thousand chances of destruction in the earlier period 

 of their existence; at a more advanced age, they 

 usually serve for the food of higher forms of animals. 

 Hence nature has provided largely for their multi- 

 plication. Many of them literally become trans- 

 formed into ovigerous sacs. Thus, for instance, in 

 the case of a Nemertes, measuring from eight to ten 

 feet in length, we cannot estimate the number of 

 ova at less than four or five hundred thousand. 



It may be readily believed that I devoted myself 

 with no common ardour to these attractive studies, 

 the pursuit of which was almost hourly attended 

 with renewed successes. At Brehat, moreover, I 



