No. 3.] ZHE EMBRYOLOGY OF THE EARTHWORM. 421 
separately from the glandular part of the nephridium. To quote 
his own words (fc. p. 654): ‘Alle bleibenden Nephridien 
entstehen zu einer Zeit, wenn das Peritoneum in der bereits 
segmentirten Larve im Allgemeinen schon den histologischen 
Charakter angenommen hat, den es bei den erwachsenen Thieren 
besitzt. Aus faltenartigen Erhebungen desselben, welche sich 
gegen die gesonderte Anlage des Nephridialschlauches hin 
nach hinten ausstiilpen, mit den letzteren in Verbindung treten 
und sich mit einem inneren Wimperbesatz bekleiden, gehen die 
Trichter hervor; die Schlauche dagegen bilden sich aus retro- 
peritonealen, anfangs soliden Zellstrangen, die nach ihrer Verei- 
nigung mit den Nephrostomen einen flimmerden, terminal nach 
aussen durchbrechenden Achsencanal erhalten und zu zweischen- 
keligen Schleifen auswachsen.” At page 663 he expresses the 
opinion that “die Nephridialschlauche einem retroperitonealen 
Gewebe entstammen und somit von den Peritonealtrichtern 
morphologisch verschieden seien,” and adds that a similar mode 
of development is characteristic of the development of Psygmo- 
branchus. Meyer does not commit himself to any definite state- 
ment as to the origin of the retroperitoneal cells, but promises 
to discuss this question in a future work. 
In his second paper (No. 36, pp. 463-476) Meyer describes in 
detail the development of the nephridia in Psygmobranchus. 
The funnel is here shown to be derived from the anterior 
(mesoblastic) wall of the dissepiment (p. 472), while the glan- 
dular part arises from a single “retroperitoneal” cell which is 
at first wholly separate from the funnel and only secondarily 
comes into connection with it (p. 468). The origin of the 
retroperitoneal cells still remains however in doubt. 
In 1886 (No. 51) Whitman announced the important dis- 
covery that the nephridia arise in C/epszne from a longitudinal 
cell-cord on each side of the body, which lies between the 
ectoblast and entoblast and forms part of the middle stratum 
of the germ-bands described by Metschnikoff many years before 
(No. 34). These cell-cords are derived from two large cells 
(nephroblasts) on each side the body, which arise from the same 
basis as the neuroblasts. 
In 1887 I showed (No. 54) that in Lambricus the nephridia 
likewise arise in connection with a longitudinal nephric cord 
‘ that is obviously homologous with the corresponding structure 
