1895. NOTES AND COMMENTS. 163 



towards the exterior, sometimes breaking directly through, sometimes 

 meeting shght invaginations of the epiblast, sometimes fusing into 

 longitudinal ducts. These centrifugally developing peritoneal ducts 

 or funnels are the genital ducts and have nothing to do with true 

 nephridia. They are to be found in the vast majority of ccelomates: 

 in oligochffites, for instance, as the oviducts and vasa deferentia ; in 

 vertebrates as the tubules of the pronephros. 



True nephridial tubules are structures of another kind. Typically, 

 they develop centripetally from outside inwards, and favour the 

 suggestion that nephridia primitively were skin excretory organs. 

 In actual development each arises as a single large cell, the interior 

 of which develops a vacuole with a tuft of cilia — in fact, becomes a 

 flame-cell, like those which flicker under the microscope when a live 

 turbellarian is examined. From the flame-cell a tail of small cells 

 grows towards the outside, and a duct is hollowed out in the thick- 

 ness of these cells. Complications arise in two ways. In many 

 cases, for instance in the common earthworm, these nephridia break 

 into the ccelome, the flame-cell becoming the nephrostome, and the 

 whole structure assuming a false analogy with a peritoneal funnel. 

 Such a false analogy, Mr. Goodrich thinks, has led many inves- 

 tigators to derive peritoneal genital ducts from nephridia. The 

 second complication occurs in such cases as the vertebrates, where 

 the primitive peritoneal ducts assume excretory functions and become 

 comparable with nephridia. Just as the nephridia in some cases 

 have broken into the ccelome and so have posed as peritoneal funnels, 

 so peritoneal funnels have occasionally assumed excretory functions 

 and posed as nephridia. In the latter categorj^ are the pronephric 

 tubules of vertebrates. 



Mr. Beddard's Monograph. 



Some time ago we received from the Clarendon Press a copy of 

 Mr. Beddard's beautiful Monograph on the Oligochaeta. We are 

 glad to say that Professor Franz Vejdovsky has promised to write a 

 detailed notice of the work for our columns, and our readers will thus 

 have the opinion upon it of the greatest continental expert. As most 

 naturalists are aware, Mr. Beddard has been working on Oligochaetes 

 for the last fifteen years, and has contributed largely to our knowledge 

 of the group. The cost of the illustrations of the volume has been 

 largely defrayed by the generosity of Mr. J. P. Gassiot, F.Z.S., who, 

 at the suggestion of the Secretary of the Zoological Society, placed a 

 sum of ;^ioo at Mr. Beddard's disposal for the purpose. The 

 Clarendon Press have published the volume in a sumptuous fashion ; 

 and it forms a notable addition to the list of modern scientific 

 monographs. 



The first part (148 pages) deals with the anatomy of the group : 

 there is not yet enough material for a systematic account of the 



