No. 3.] THE EMBRYOLOGY OF THE EARTHWORM. 419 
X. ExcrETORY ORGANS. 
The following account of the development of the nephridia 
will be facilitated by a short review of our present knowledge 
of the subject. For the sake of brevity I shall pass over most 
of the earlier literature and consider only the results of more 
recent studies. (For fuller reviews of the literature, see Vejdov- 
sky, No. 44; Bergh, No. 8; Eisig, No. 16; and Meyer, No. 35.) 
The development of the nephridia in the Polychaeta has been 
most carefully studied by Meyer, to whose interesting work 
reference will be made further on. Our present knowledge of 
the nephridia in the Oligocheta rests in the main upon the 
beautiful researches of Vejdovsky, whose great work on the 
Oligochzeta (No. 44) must long remain a standard work of refer. 
ence for students of annelid morphology. 
Vejdovsky has clearly demonstrated the fact, suspected by 
Kleinenberg (No. 28) and definitely asserted by Bucinsky (No. 
9), that the permanent nephridia in the Oligochzeta arise from 
two sources, their inner portion being formed in the somatic 
mesoblast, their outer portion (‘Endblase’’) arising as an ecto- 
blastic invagination. According to these authors the ectoblas- 
tic portion comprises only the so-called muscular part of the 
nephridium, while the glandular and ciliated portions, with the 
peritoneal funnel, are formed from the mesoblast. 
Vejdovsky has shown, moreover (No. 46), that in the course of 
the embryonic development of Oligocheta (Rhynchelmis, Lum- 
brictd@), no less than three sets of excretory organs are formed, 
apparently quite independently of one another. The first of 
these are the well-known “ Schluckzellen,” a short account of 
which has been given at p. gor. By Hatschek they were sup- 
posed to be concerned in the ingestion of albumen by the young 
embryo. Vejdovsky has, however, shown them to be connected 
with a system of delicate ciliated canals which lie in the space 
between the ectoblast and entoblast, and communicate with the 
outside through pores in the Schluckzellen ; the latter structures 
are therefore undoubtedly to be regarded as larval organs of 
excretion. They wholly disappear in later stages. 
The “larval excretory organs”’ are succeeded by indepen- 
dently developed “provisional” or “embryonal” organs (pro- 
nephridia) which are almost certainly homologous with the 
