ZOOLOGY AND BOTANY, MICROSCOPY^ ETC. 57 



one. The body gives off secondary fibres which unite with those from other 

 cells, and the bipolar becomes a multipolar cell. " In no case do nerves 

 from the central system unite directly with the sense-cells. All the nerve- 

 endings in the hypodermis mark approximately the places where the 

 ganglionic cells originated. The latter alone are directly united on the 

 one hand with the hypodermis, and on the other with the central nervous 

 system. The nerves must thus terminate between cells, and probably 

 extend to their very outer ends." Sense-cells occur, however, apparently 

 terminating in a single fibre, which does not extend along the walls. In 

 this connection Patten notes that while the ordinary epithelial cells which 

 by their root-fibres form the basal membrane, probably homologous with 

 myo-epithelial cells of Coelenterates, the sense-hair cells, which terminate 

 in a single fibre, are homologous with the neuro-epithelial cells. The 

 inward prolongations of the sense-cells in the MoUusca are not then nerve- 

 fibres, arising either from the nervous system or from peripheral ganglionic 

 cells, but are simply nervous prolongations of the sense-cells themselves, 

 and are probably united at their inner ends with a contractile one which 

 originated near the sense-cell, and which during its inward growth has 

 drawn the nervous fibre of the latter after it. The sense-cells have inter- 

 cellular nerve-fibres like the ordinary epithelial cells. The central nervous 

 system arose like the peripheral ganglion cells. As the ganglion cells of 

 a single sense-organ became connected, similarly do the ganglia of remote 

 sense-organs become connected with the central system. In the origin of a 

 sense-organ from a group of hypodermic cells, the increase of nerve-cells 

 is associated with increasing sensitiveness, and finally gives rise to a 

 subjacent layer of ganglion-cells united on the one hand with the central 

 nervous system, and the other with the sensitive cells, between which the 

 ganglionic ones have arisen. We find abundant transitions between sensory 

 and ganglionic cells. 



"Liver" of Mollusca.* — In this communication on the so-called liver 

 of the Mollusca Dr. J. Frenzel reports that he has made a histological 

 examination of a number of species ; in the Cephalopoda, and probably 

 also in some Prosobranchiata, there is only one kind of epithelial cell, 

 which is comparable to the club-shaped ferment-cells of other molluscs ; 

 in these forms the " liver " must be regarded as a digestive gland. In a 

 number of Prosobranchiata the epithelial cells are of the granular character, 

 and here, on Barfurth's showing, the organ must be considered to be a 

 true liver. In the Opisthobranchiata the gland has two kinds of secreting 

 elements, and may, therefore, be a " hepatopancreas." 



As, notwithstanding all their differences, the livers of Mollusca have 

 so many histological details in common, the author thinks the organ must 

 have a common function ; the suggestion of Barfurth that it gives rise to 

 glycogen seems to be disposed of by the answer that glycogen is especially 

 found in young, developing cells, and that such cells are always to be found 

 in abundance in the moUuscan liver. It is well to retain for the organ the 

 name of midgut gland. 



Nervous System of Gastropoda.f — Prof. H. de Lacaze-Duthiers points 

 out that in studying the nervous system of Mollusca we ought to seek to 

 recognize the primary so as to distinguish them from the secondary ganglia. 

 This may be illustrated by the innervation of the digestive tube of some 

 of the Gastropoda. Here the oj-igin of the cerebrosympathetic connectives 



* Boll. Soc. Adriat. Sci. Nat. Trieste, ix. (1886) pp. 226-39. 

 t Comptes Eendus, ciii. (1886) pp. 583-7. 



