112 NEMERTINEA 



to the muscular layers, and are connected together throughout by 

 a plexus. Xo nerve branches are 

 given off. The brain is not divided 

 into lobes. The cephalic slits are 

 only represented by a shallow depres- 

 sion on each side of the head, and 

 110 canals have been observed leading 

 from them. The intestine is straight, 

 and the pouches are usually absent 

 or rudimentary. The circulatory sys- 

 tem is largely made up of lacunar 



specimen, slightly contracted, little developed. 



S^SSkTSTS Principal British genera and 



posterior end. SpeClCS : - 



Carinella annulata Mont, C. linearis (Mont, MS.) M'lnt, 0. macintoshi 

 Burger (Fig. 59), C. polymorpha, Ren. 



Cephalothnx bioculata Oerst., (7. linearis Ratbke. 

 Valencinia limformis M'lnt 



A most important monograph by Burger l on Nemertines has 

 just been published, but unfortunately it appeared too late to 

 lie adequately considered here. He gives an elaborate account, 

 illustrated by admirable figures, of the present state of our know- 

 ledge of this group, and his work will be indispensable to future 

 students of the subject. The older systems of classification are 

 criticised, and the following scheme is adopted in their place : 



ORDER I. PROTONEMERTINI ( = part of the Palaeonemertea, 

 e.g. Carinella}. The brain and lateral nerve-cords lie outside the 

 muscle layers in the epithelium or below the basement membrane. 

 The body-wall consists of the following layers: epidermis, base- 

 ment membrane, circular muscles, and longitudinal muscles. The 

 mouth lies behind the brain. The proboscis is unarmed. 



ORDER II. MESONEMERTINI ( = part of the Palaeonemertea, 

 e.g. Cephalothrix). The characters of this Order are similar to 

 those of the Protonemertini except that the brain and lateral 

 nerve-cords lie in the muscle layers. 



ORDER III. METANEMERTINI ( Hoplonemertea). The brain 

 and lateral nerve -cords lie in the parenchyma of the body 

 internal to the muscle layers. The layers of the body-wall ai-e 



1 Fauna mid Flora G. ron Xwpcl, '22 Monogr. 1895. 



