38 SUMMARY OF CURRENT RESEARCHES RELATING TO 



cavity ; the hepatic lobes are hollowed out, and the ansae project con- 

 siderably. The ventral surface is distinguished by the pedal process, 

 at its anterior end. Eight and left of the mouth there lie two ecto- 

 dermal elevations, which may be known as the sensory plates ; from 

 these the cerebral and pleural ganglia of either side are developed ; 

 a ventral median growth gives rise from before backwards to two 

 pedal, two visceral, and one abdominal ganglion. The first of these 

 are only secondarily connected with the cerebral and pleural ganglia ; 

 the connection between the separate pairs was primitively effected by 

 the median outgrowth, but this becomes lost, and a secondary connec- 

 tion takes its place. The pair of buccal ganglia arise from the oeso- 

 phagus, and the olfactory ganglion is either developed on the right 

 or in the dorsal median line. Attention is directed to the resem- 

 blances and the differences which obtain between the development 

 of the nervous system of Bithynia and that of an Annelid. 



The larval heart lies a little to the right side of the neck ; the 

 permanent heart may be seen to pulsate during its existence, but 

 the pulsations are not synchronous. At the same time as that of the 

 development of the nervous system, an ectodermal thickening on the 

 right side of the embryo gives the first indication of the permanent 

 kidney ; under the effects of torsion, this organ comes in time to lie 

 on the left side ; at the same time, it elongates and becomes hollow. 

 The pericardiac cavity is formed by mesodermal cells which become 

 contractile, and from the solid cord of cells within it the permanent 

 heart is formed ; this lies almost perpendicularly to the kidney. 



With regard to the germinal layers, the author tells us that the 

 ectoderm is remarkable for never being at rest during the develop- 

 ment of the embryo; all the organs are formed either directly or 

 indirectly from it; the mesodermal elements do not arise at any 

 definite and single point, and there is no evidence of any cleavage in 

 it, and still less of the formation of a true coelom. As the endoderm 

 so called does not give rise to the enteron, its homology with the 

 similarly named layer in the chick is to be doubted. 



Many of the author's statements could only be made clear by the 

 reproduction of a number of his figures. 



Organization of Adriatic Chitons.* — B. Haller has examined 

 chiefly Chiton siculus and C. fascicularis. Commencing with an 

 account of the nervous system, he finds that, in the oesophageal ring, 

 the primary pallial and pedal nerves form a connected whole, in 

 which ganglia and commissures are not yet differentiated ; any given 

 transverse section exhibits a cortical layer of ganglionic cells, pro- 

 cesses from which are either continued directly into the central nerve- 

 plexus, or pass directly into the nerve-trunks. In the nervous system, 

 and, especially, in the region of ganglionic cells, we may observe the 

 well-known orange-yellow coloration, which is most intense where 

 the cells are most largely aggregated. The nerves of the upper 

 cesophageal ring either supply the cephalic portion of the mantle, or 

 belong to the cephalic lobes, or innervate the lips, the epithelial layer 



* Arbeit. Zool. lust. Witn, iv. (1882) pp. 323-9G (8 pis.)- 



