316 SYNOPTIC COLLECTION. 



characters indicate secondary and not primary condi- 

 tions. 



The group is represented in the Synoptic Collection by 

 Cerebratulus, Meckelia, and Borlasia. 



Cerebratulus marginatus (No. 783) , has an extremely 

 long body which is indistinctly segmented. The forward 

 end is small and a long slender organ, the proboscis, 

 which is characteristic of the Nemertines, extends from 

 it (PI. 784, C. tristis Hubr.). The figure shows that this 

 proboscis is not thrown out of the mouth but has a sep- 

 arate opening above the mouth. It is provided with a 

 sheath and sharp spines and is thought to be an organ of 

 defence. The head also possesses deep lateral slits or 

 olfactory organs. 



There are no locomotive organs on the sides of the 

 body. It is generally stated that these worms move by 

 the cilia which cover the whole body, but according to 

 MTntosh, 1 this statement is incorrect. This author 

 maintains that the adhesion of the body to the mucus 

 which is secreted by the worm gives the animal sufficient 

 purchase for the use of its facile muscles, so that it is 

 muscular rather than ciliary action which causes locomo- 

 tion. Many of these worms, however, lie for hours in 

 what would seem to be a torpid state, and Cerebratulus, 

 although a good swimmer, has the habit of frequenting 

 empty bivalve shells in which it remains quiescent. 



Meckelia macrorrhochma Scrim. (No. 785, model), is 

 large in the anterior region but is without a distinct head 

 and the body tapers posteriorly. It is without external 

 locomotive or respiratory organs. Like Cerebratulus it 

 possesses the proboscis enclosed in a sheath which has a 

 distinct opening just above the mouth. 



Other Nemertean worms are Borlasia trilineata Schm. 

 (No. 786, model), and Nemertes flaccida O. F. Mull. (No. 



1 Monograph on Brit. Annelids, part i, 1873, p. 6. (Ray 

 Society.) 



