136 Chronicles of Science. [Jan., 



has indicated certain general laws which contrast strikingly with facts 

 universally recognized in other groups. The swimming and tubico- 

 lous Annelids constitute in salt water the geographical term corres- 

 ponding to the land and fresh water Lumbrici and Naiades. The 

 marine class has representatives in all seas, and this cosmopolitism 

 belongs not only to the large genera which best reproduce the general 

 type, but also to the most exceptional sub-types. Hence the Annelidan 

 Fauna does not present anything resembling zoological regions, such 

 as have been demonstrated for most of the other classes of animals. 

 While there is a tendency to diffusion in the genera, there is a counter- 

 balancing tendency to restriction in the species, and none, or scarcely 

 any of the latter, are common to two continents or hemispheres. 

 Exceptions are probably due to marine currents, as the gulf streams, 

 whicb he supposes may convey a species from the West Indian seas 

 to the Indian Ocean. The corresponding geographical terms, there- 

 fore, must only be sought among species. Equality of organization is 

 one of the most general laws of th<; group ; it does not present the 

 difference corresponding with the latitude which are found in the 

 Crustacea, for example. And finally, the nature of tbe coast has the 

 most influence upon the development of the Annelidan Fauna, granitic 

 and schistose coasts being generally remarkably rich in species and 

 individuals, while calcareous coasts are remarkably poor in both. 



M. Hesse has described a remarkable apparatus in parasitic Crus- 

 tacea, which he denominates the frontal cord, and which he supposes 

 to be an important organ of conservation in these apparently helpless 

 creatures. This curd is very flexible, especially in its middle part; 

 hollow, cylindrical, and covered with a few hairs. By this cord the 

 embryo is united with its mother, being attached by one extremity to 

 the frontal margin of the young, and by the other to the body of the 

 mother Crustacea by a circular dilatation, and is sufficiently long and 

 flexible to allow the young Crustacea to act, to a certain extent, inde- 

 pendently of its mother, and to apply itself to the fish, on which they 

 live in common. These embryos, especially those attached to the 

 Trebice and Caligi, which swim with tolerable rajndity, follow the 

 evolutions of their mother, like a little boat towed along by a larger 

 vessel ; and M. Hesse is of opinion that the object of this apparatus is 

 not the alimentation of the embryo, but to assist it while feeble and 

 destitute of organs of adhesion, to maintain its position, and resist the 

 action of the waves during the progression of the fish on which it is 

 parasitic. 



M. Sars has made some curious observations upon the persistence 

 in the Scandinavian lakes of certain marine Entomostraca of the 

 glacial epoch. Harpacticus chelifer was found in a fresh-water lake 

 in the neighbourhood of Christiansund. In the Mjoesen lake, the 

 largest in Norway, he discovered two species of Cythere, Mysis relicta 

 (Lov.), and Gammarus cancelloides (Gerstfeldt) ; the two latter 

 species were also found by Loven in the Swedish lakes. In ponds of 

 the environs of Christiania the amphipod, Pontoporeia affinis, was 

 discovered. These species all inhabit the deepest parts of the water, 



