ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 39 



are therefore nephroblasts ; the ultimate fate of the remaining pair of 

 rows has not yet been made out. 



The neuroblasts fit closely into the ectoblast, and in some cases 

 unquestionably extend to the outer surface. The ventral nerve-cord is 

 formed by the gradual concrescence of the neural rows in the median 

 line ; there is no invagination from the exterior, and the continuity of 

 the ectoblast across the median line is never broken. Unless there is 

 a great difference between L. rubellus and L. olidus, Dr. Hatschek must 

 have mistaken the narrow angular interval between the converging 

 halves of the cord as evidence of invagination. 



The nephridia and their nephroblasts have a very similar history to 

 the nerve-cord and neuroblasts ; the nephridia arise as paired metameric 

 outgrowths from the nephridial rows, and there is in each somite a 

 single pair. 



The mesoblastic bands arise as single rows of cells at the latero- 

 posterior angle of the mesoblasts, curve round their outer sides so as 

 nearly to meet in the middle line, then bend rather abruptly outwards 

 and run forwards ; they soon become broad bands that pass between the 

 endoblast and the remaining six cell-rows. They give rise to all the 

 muscles and vessels of the body, as well as to the ciliated funnels and 

 outer investments of the nephridia. Not only the neuroblasts, but also 

 the nephroblasts and " lateral teloblasts " appear to be modified ecto- 

 blastic cells. Prof. Wilson cannot doubt but that the nephroblasts are 

 derivates of the outer germ-layer, and thinks, consequently, that the 

 likeness between the development of the nephridial row and that of the 

 segmental duct of vertebrates (as recently described by Spee and 

 others) is very significant, for in the rabbit, the guinea-pig, and Raja, 

 the segmental duct has been found to arise as a solid cord of cells that 

 is split off from the outer layer, and grows at its hinder end by the 

 proliferation of a limited area of the ectoblast. The conclusion is 

 arrived at that the " nephridial row " of Lumbricus must be regarded as 

 homologous with the segmental duct, and the series of nephridia as 

 homologous with the vertebrate pronephros. 



The likeness between the germ-bands of Lumbricus and Clepsine seems 

 to indicate a very close relationship between the Oligochasta and the 

 Hirudinea ; the development of the six anterior teloblasts in Lumbricus 

 may be explained as due to the greater and greater concentration of 

 developments at the posterior ends of the germ-bands ; they are at first 

 ordinary ectoblast cells which afterwards sink below the surface. In 

 Clepsine they are covered by the ectoblast at a very early stage owing 

 to acceleration of development. 



Photodrilus phosphoreus, Type of a New Genus of Phosphorescent 

 Lumbricids.* — M. A. Giard establishes a new genus for the Lumbricus 

 phosplwreus of Duges. It was observed by him at Wimereux, and the 

 light was seen in points of a fine opalescent green. The luminous points 

 were of unequal size, the largest giving a light as bright as those of the 

 Lanipyridae, and being visible even in a well-lit room. If one of the 

 points was rubbed between the hands, the two palmar surfaces were for 

 a short time luminous, and near each point a small earthworm was 

 found. Photodrilus phosphoreus is 45 to 50 mm. long and about 1 ■ 5 mm. 

 wide; it has about 110 segments; the skin is very transparent and 



* Comptee Rendus, ev. (1887) pp. 872-4. 



