CURRENT LITERATURE. 89 



occasioned, first a compression, and then a displacement of the anus and the 

 intestine leading to it ; the position of the anus moved gradually to the fore part 

 of the right side, while the shell settled clown more to the rear of the animal. 

 This displacement of the anus was mainly produced by an arrest of growth 

 affecting the entire right side of the body in a narrow space situated immediately 

 beneath the pallial border, from the mouth to the left branchia. This torsion of 

 the anus occasioned a twist of the branchiae through 180 , the original left 

 branchia becoming the right, and vice versa, while, as regards the nerves, the 

 visceral commissure, being involved in the twist, since it lay over the intestine, 

 became crossed or chiastoneurous. Observations of the growth of the embryo, 

 particularly those of von Erlanger on Paludina, tend to confirm the truth of this 

 rather complicated hypothesis. 



Not the least interesting of the matters dealt with in this very important paper, 

 is a most ingenious explanation of a well-known but obscure phenomenon which 

 occurs in some species on our own shores, viz., the occurrence, in a dextral shell, 

 of a sinistral embryonic form at the apex. This is the case with Odostomia, 

 Eulimella, Turbonilla, Mathilda, with a few Opisthobranchs (Acttson, Tomatina, 

 Actaonina), and with one genus of Pulmonates [Melampus), It is suggested 

 that in these genera the embryonic shell was, as is obvious, sinistral, but that at 

 a given period, for some unexplained reason, it changed, little by little, the 

 direction of its inclination in relation to the axis of the body, and so became 

 dextral. 



These are but a few of the points dealt with in this extremely important and 

 admirably-written article, which is sure to give occasion to further discussion of 

 the theories therein set forth. — A.H.C. 



The Anatomy of Siphonaria gigas, Less. (Arb. Zool. Inst. Wien, x. i, 

 pp. 71-100, 3 plates, 1S92.) 



Herr B. Haller's lucid and valuable paper will repay careful study by every 

 morphologist interested in the Gasteropoda. Siphonaria, which has been 

 variously regarded as a Limpet and as a I'ulmonate, he shows, by a complete 

 anatomical investigation, to be an Opisthobranch, nearly allied to the Umbrellida, 

 but more primitive in many of its characters than any other member of the 

 Opisthobranchia. The resemblance of its shell, foot, and pedal musculature to 

 those of Patella he very conclusively demonstrates to be homoplastic, — an 

 adaptation to a similar sedentary life upon rocks. 



Cerebral ganglia connected by unusually long cerebral commissures. Cerebro- 

 pedal, cerebro-pleural, and pleuro-pedal commissures very short and stout, but 

 quite recognisable. Several enormous ganglion-cells occur on main ganglia, as in 

 other Opisthobranchs with concentrated central nervous system : apparently 

 bipolar in cerebral, unipolar in pleural ganglia, — poles prolonged into the various 

 commissures. Two pedal commissures, one behind other : but anterior com- 

 missure seems to be a mere pedal chiasma, where fibres of inner pedal nerves 

 cross over into ganglia of opposite side. Two anterior visceral ganglia, con- 

 nected with pleurals by long, stout commissures which pass through the cerebrals, 

 as in Prosobranchs. A single posterior visceral ganglion lies asymmetrically 

 behind right pleural, and is connected with it and with left pleural by short com- 

 missures. Innervation of various organs is fully described. 



There are two hard jaws (carnivorous) ; radula myrioglossate, resembling 

 especially that of Umbrellidce. Crop large and long (contained Ophiurids). 

 Stomach small, spherical, receiving two hepatic ducts. Intestine long. Rectum, 

 deep black colour ; anus, middle ot right side. 



Mantle-cavity of large horizontal extent ; opening in middle of right side by 

 a small aperture (adaptation to rock-life). 



Nephridia two : one right, one left. Right nephridium entirely in roof of mantle- 

 cavity : ureter on its right side, on level with anus ; no certain connection with 

 pericardium. Left nephridium larger than right, bilobed, — one lobe in roof, one in 

 floor of mantle-cavity; the common duct opens on left side of cavity, between it 

 and pericardium, after first giving off a short funnel which opens into left corner 

 of pericardial chamber. The presence of two nephridia in Siphonaria is an archaic 

 character, unique among Opisthobranchia. The smaller size and absence of 

 nephrostome perhaps point to incipient degeneration of right nephridium. 



