SENSE ORGANS VASCULAR SYSTEM IOJ 



are a few long hairs scattered sparsely among the cilia of the 

 epidermis. 



Frontal Organ. In many Nemertines there is present at the 

 anterior tip of the head a disc-shaped group of cells bearing long 

 hairs or bristles. On this disc open the secreting ducts of a 

 number of gland cells lying in the head. It seems possible that 

 this frontal organ may function as an organ of taste. 



Side Organs. In the Carinellidae there is a pair of circular 

 epithelial patches lying one on each side of the body in the 

 region of the excretory pore. The cells composing them are 

 richly ciliated and provided with a plentiful nerve-supply. The 

 function of these epithelial patches is not known, but it has been 

 suggested that they may be auditory organs. 



Cephalic Slits and Cerebral Organs. In most Nemertines 

 there is a peculiar pair of organs (Figs. 50, 53, c.s), situated in 

 the head and in close connexion with the brain. The function 

 of these organs is not known. Hubrecht has suggested that they 

 may be respiratory, while Burger 1 conjectures that they may be 

 organs which are used for discriminating the condition of the 

 surrounding medium. In an external examination of the 

 head, the cephalic slits may usually be seen as a pair of lateral 

 furrows or pits. Their form and direction vary considerably ; 

 they may take the form of shallow circular depressions, or they 

 may lie longitudinally and be slit -like in shape (Fig. 50), or 

 the slit may lie at right angles to the long axis of the body and 

 be beset with short transverse furrows. In some forms these 

 slits are merely superficial depressions, but in others they are 

 continued into ciliated ducts, which pass inwards and penetrate 

 into special lobes, consisting of glandular tissue and ganglion 

 cells, in close connexion with the brain. These lobes are called 

 the cerebral organs. 



In many forms the nervous system is charged with haemo- 

 globin, which gives to it a bright red colour. 



Circulatory or Blood -Vascular System. The circulatory 

 system consists of three main longitudinal vessels, a median 

 dorsal and a pair of lateral ones. These are connected together 

 posteriorly by a transverse trunk, and also throughout the whole 

 length of their course by branches, which are given off at 

 regular intervals. Anteriorly the three longitudinal vessels 

 1 " Nemertinen, " Fauna und Flora G. ton Xeapel, 22 Monogr. 1895. 



