286 NOTES AND MEMORANDA. 



it is also enclosed in a still larger bladder ; the walls of this invest- 

 ment are invaginated at the anterior end, so as to form an aperture 

 through which the body of the Cercaria can be protruded ; on the 

 other hand, the whole of the creature may be at times observed to be 

 retracted within this envelope. With regard to this last no explana- 

 tion is offered, but it is noted as non-existent in Cercaria macrocerca, 

 although the tail of this form has a proper investment. 



Tlie author makes some observations on the species of Buce- 

 phalus which infest members of the same division of the M(dlusca ; 

 two forms, B. polymorphus, Baer, which lives in the reproductive organs 

 of Anodon, and B. laimeanus, Lacaze-Duthiers, which is found in 

 marine forms, Cardimn and Ostrea, are already known ; a third, which 

 as standing between the other two is very appropriately named B. 

 intermedins, is now described ; it was found in Anodonta cellensis, and 

 the peculiarities of its structure are associated with its caudal region. 

 In B. polymorphus the body terminates in a compressed and more or 

 less biscuit-shaped bulbous enlargement, the broad end of which is 

 attached to the body of the worm ; the tail connected with this bulb, 

 in which, it should be said, two portions can be made out, is eminently 

 variable in form owing to its great power of contractility ; in the new- 

 species the two parts are more distinctly differentiated and are separated 

 by a constriction, but the caudal portion is constantly cylindrical in 

 shape, and its only power of change is limited to its greater or less ex- 

 tension. When several forms get together they are able to form, with 

 their tails, a veritable Gordian knot, which no instrument can unloose ; 

 in this point it differs very markedly from B. polymorpTius, the tail of 

 which can by very slight excitation be brought to change its form. 



New Turbellarian. — The sojourn of Mereschkowsky on the White 

 Sea has at any rate produced an account of a most interesting 

 Turbellarian, to which he has given the name of Alauretta viridiros- 

 trum* The body of this creature was elongated, and broadest at its 

 anterior end, and measured -^^ of a millimetre ; all but the proboscis, 

 which was green, was colourless, and fairly transparent. Seen from 

 without there appear to be three segments, owing to the presence of 

 two circular constrictions towards the posterior end. By the aid of 

 fine short cilia the animal moves about rapidly ; these cilia are found 

 over the whole body, with the exception of the very anterior region, 

 where a single seta on either side stands directed forwards and out- 

 wards. The integument is thick and is succeeded by two layers of 

 the body wall ; of these the inner one is the thicker, and is distin- 

 guished by giving off five projections into the body cavity, which give 

 an appearance of metamerism, and to which the author gives at least 

 their full weight. 



The mouth is placed in the anterior part of the body, where it 

 forms an ellipse-shaped cleft ; the enteric tube is straight, and does 

 not branch ; the position of the anus is left in a little doubt. The 

 nervous system is distinguished from that of all other Turbellaria, 

 by the possession of a large number of bipolar and unipolar nerve- 

 cells ; the eyes are on either side of the nerve-centre. 

 * 'Arch, fiir Naturgeschichte,' xlv. (1879) 35. 



