IXTRODUCTION. Iv 



evidence relied upon by Prof. Smitt and myself is affected 

 by this criticism and by later observations^ and what the 

 present state of the question seems to be. This course 

 will clearly be the most valuable to the student, as it will 

 indicate to him the directions in which further research 

 may be profitably conducted. And as, of course, the only 

 object to be aimed at in such work is the discovery of the 

 actual fact, I shall endeavour to approach the subject 

 without any controversial animus. 



i. As to the origin of the " brown body,'^ if we except 

 Claparede, who regarded it as a secretion from the en- 

 docyst^, observers are generally agreed that it is derived 

 from the substance of the polypide. As the latter, after 

 a longer or shorter term of existence, gradually fades 

 away, it gives origin to a "brown body," which remains 

 attached to the funicular cord, and more or less enveloped 

 by the plexus of threads arising from the latter. Joliet 

 would call it the mere wreck of the polypide ; Smitt has 

 named it the "germ-capsule" {groddkapsel) implying that 

 it has in it the possibilities of new life. In my papers on 

 the subject, I have held that the "brown body" is formed 

 out of the lower portion of the digestive sac, which in 

 some species (e. g. Bicelluria ciliata) has the apparancee 

 of being separated by a constriction from the rest of the 

 stomach, and constitutes, as it were, a separate chamber 

 of somewhat globular shape (Woodcut, fig. x.). This 

 peculiarity of structure I have connected with the forma- 

 tion of the germ-capsule ; but I am now satisfied that this 



* " BeitrJige zur Anatoiuie ii. Eutwicklungsgeschichte der Seebryozoen," 

 Zeitsch. f. wissensch. Zool. December 1870, p. 147. Clai^ai-ede's view must 

 be coasidered a simple corollary from bis extraordinary tbeory of the 

 '• retrogressive metamorphosis " of the polypide, rather than thci-esult of any 

 close and careful observation. 



