1 64 WHITMAN. [Vol. I. 



nephridia by metameric division of a pair of continuous longi- 

 tudinal rudiments. There can be no doubt about the homol- 

 ogy of the nephridial rows in Clepsine and Lumbricus with the 

 longitudinal "cell-strings" of Criodrilus; and the ciliated pos- 

 terior ducts, which appear to develop as sprouts from the " head- 

 kidneys " in Polygordius, are only more highly developed forms 

 of the simple nephridial rows I have described. 



Nephroblasts were not discovered in Criodrilus, but we may 

 now be almost certain that they are present. We may be 

 equally confident, I think, that nephroblasts, or equivalents, are 

 present in Polygordius. Until they are discovered and their 

 exact relations to the "head-kidneys" made out, it will be 

 difficult to decide the question as to the strict identity of the lar- 

 val nephridia in the Gnathobdellidae with the cephalic nephridia 

 of marine annelids, such as Polygordius, Echiurus, Eupomatus 

 (Serpula), etc. 



Balfour (No. 32, p. 567) was very decided in the opinion 

 that " the provisional excretory organs of the leeches cannot 

 be identified with the anterior provisional organs of Polygordius 

 and Echiurus." The question now stands in a somewhat different 

 light. Vejdovsky (No. 31, pp. 1 21-122) has discovered larval 

 excretory organs in Rhynchelmis, Aeolosoma, Nais, and Chae- 

 togaster, and thinks it probable that they occur in the early 

 embryonic stages of all the Oligochaeta. Bergh has traced the 

 development of such organs in the leeches ; and his observations, 

 in connection with mine, make it almost certain that both the pro- 

 visional and the; permanent organs arise from the same cell-cords. 

 Wilson has made the important discovery of nephric cell-cords in 

 Lumbricus ; and this, in connection with the wide-spread occur- 

 rence of teloblasts, leaves little room to doubt that such cell- 

 cords are common to all annelids. The case is made still 

 stronger by the earlier observations of Hatschek on Polygordius, 

 Echiurus, and Criodrilus, and by E. Meyer's discovery (No. 33, 

 p. 6']^^ of a longitudinal canal connecting the permanent 

 nephridia of Terebella (Lanice) conchilega. The general oc- 

 currence of these larval organs, their relatively early origin 



(32.) Balfour, F. M. Comparative Embryology. II. 1881. 



(33.) Lang, Arnold. Die Polycladen. Fauna und Flora des Golfes von 

 Neapel. Monographic XI. 1884. 



