BRITISH NEMERTEANS, AND SOME NEW BRITISH ANNELIDS. 307 



scopic structure of the proboscis, as well as to advance our knowledge of the 

 minute anatomy of these animals and their immediate allies. 



I use the terms Ommatopleans and Borlasians provisionally in the mean- 

 time, because the majority of these soft animals group themselves round two 

 centres, represented respectively by the common Ommatoplea alba and Borlasia 

 olivacea. The terms, indeed, are nearly equivalent to Max Schultze's Enopla 

 and Anopla, and to Prof. Keferstein's Tremacephalidw and Rhochmocephalidae. 

 I do not think it advisable to call by the name of Borlasia, as the last-mentioned 

 author has done, a family whose structure is quite different from that of the 

 animal originally so termed, and hence I have preferred Ehrenberg's name, 

 Ommatoplea, on the one hand, and substituted Borlasia for Keferstein's Nemertes, 

 on the other, both because it {Borlasia) has the priority, was applied to an animal 

 similar in structure, and because there are strong claims to perpetuate the name 

 of the early English zoologist. So comprehensive are the above terms, that 

 almost in every minute particular all the known British forms, with the exception 

 of Cephalothrix and another, resolve themselves at once under their respective 

 heads. 



Ommatoplea alba (and variety rosea) may, as above mentioned, be con- 

 veniently taken as the type of the Ommatoplean group, both from its size and 

 abundance, and accordingly a systematic examination of its anatomy shall first 

 engage our attention, the additional observations made on its immediate allies 

 being appended and contrasted therewith. It is also fair to state, that I could 

 not have pursued the following inquiries if a liberal and ever-ready supply of 

 living animals from the St Andrews' rocks had not been perseveringly forwarded 

 by a relative, to whom I owe the deepest obligations in this and other depart- 

 ments of zoology. 



Dermal Tissues. — The body of the animal, like that of each in the Order, is 

 universally covered with cilia, some longer ones being present at the proboscidian 

 aperture and mouth, and others at the tip of the tail. The ciliary motion is most 

 active at the openings of the cephalic pits. In Tetrastemma variegatum, it is in- 

 teresting to watch the cilia at the anterior end, especially around the aperture of the 

 proboscis, as the long cilia bend outwards and inwards with a less rapid motion 

 than the shorter. Those at the posterior end cause a complete vortex, the longer 

 cilia often remaining quiescent. The granules in the surrounding water are directed 

 by the cilia of the sides of the tail towards the tip, where, after coming in contact, 

 the two opposing currents dash outwards, frequently again to curve round, and 

 cause their granules to come under the action of the lateral cilia. The whole 

 appearances very much resemble the currents of water in a vessel after the 

 application of heat. This action would be of little service to an animal whose 

 posterior end was quite closed. The cilia, as long known, perform a respiratory 

 function ; at least there exist no other special organs for the purpose. 



