vii ANNELIDA 157 



blastopore persists as the mouth, and the embryonic gut becomes 

 swollen and globular owing to the ingestion of the nutritive material, 

 the albumen, with which the embryo is surrounded. 



The question of the origin of the nephridia in Annelida is a 

 subject which has been much worked at in Oligochaeta where, owing 

 to the fact that the eggs are contained in quantities in a cocoon, all 

 stages of the embryo up to those that show all the adult features, can 

 be obtained in quantity. The original conception of a nephridium 

 as a tube connecting the coelom with the exterior, governed the 

 early investigations into the subject. Bergh (1899) and Biirger 

 (1902) asserted, that in Oligochaeta the nephridium arose as a 

 growth of the septal wall of the coelom, that it gave rise to a 

 chain of cells projecting backwards, which eventually fused with the 

 ectoderm and then became hollowed out, so that the whole nephridium 

 is to be looked on as a " tail " of the coelom. Moreover since the 

 first trace of a cavity appears in the funnel region and is a prolonga- 

 tion of the body-cavity, the cavity of the nephridium might be said 

 to be part of the coelom. 



This view was attacked by Goodrich (1897-1898), who showed 

 that in certain Polychaeta (cf. Nepthys) the nephridia do not open 

 into the coelom at all but terminate internally in a bunch of 

 solenocytes which project into the coelom. He regarded the 

 nephridium as essentially an ectodermic structure, and as comparable 

 with the excretory tube of a Nemertine or of a Platyhelminth. He 

 believed that in a great many Annelida these blind nephridia had 

 secondarily acquired openings into the coelom, but that on the other 

 hand there were other so-called nephridia, cf. the large anterior 

 nephridia of Terebellidae and Arenicolidae and the nephridia of 

 Mollusca and Peripatus, which did actually develop as outgrowths 

 from the coelom, and which in consequence he termed coelomiducts. 

 Goodrich regards the excretory organs of Oligochaeta as "true" 

 nephridia not coelomiducts, i.e. as tubes originally blind which have 

 acquired secondary communications with the coelom, and he pointed 

 to the coexistence of the genital duct (which is a wide short 

 coelomiduct) and the nephridium in the same somite, in Lumbricus, 

 as evidence that the two structures cannot be homologous with one 

 another. Evidently the question as to which category these nephridia 

 belong can only be answered by renewed and exhaustive research 

 into the mode of their development. 



This has been done by Staff (1910) in the case of the worm 

 Criodrilus lacuum. A word or two on Staff's method's may be in 

 place here. Criodrilus lacuum is a worm which inhabits swamps on 

 the banks of the Danube. In May and June when the swamps are 

 nearly dry its cocoons are found attached to the stalks of the grasses 

 growing in the swamp. These cocoons are collected, and they are 

 then pressed at one end and the contained embroyos are thus 

 squeezed out. They are preserved in " Eisig's mixture." Then they 

 are examined under a strong dissecting microscope, and slit open 



