INTRODUCTION. XClll 



is unaffected by those observations. There can be no 

 doubt that the ova generated in the zooecium do pass 

 into the ovicell and there ripen into the perfect larva, 

 escaping at last through its orifice. The ooecium is thus 

 both a brood -chamber and the passage for the embryo 

 from the cell to the surrounding water. 



But whilst I have no doubt that the ovicell acts as a 

 kind of marsupium, there seem to me to be grounds 

 for believing that in some cases, and under conditions 

 which I cannot explain, ova are also produced within it. 

 Reid long ago described the ooecial ova as adhering in 

 their earliest stage to the lining membrane at the upper 

 end of the capsule. I have repeatedly observed in the 

 ovicell a minute and somewhat indefinite mass of gra- 

 nular substance in contact with the membrane at the top 

 of it, which had all the appearance of a nascent ovum ; 

 the first change seemed to consist in a slight concentration 

 of the matter towards the centre of it. In other ovicells 

 there was a small circular body ; in others the ovum had 

 increased in size, and exhibited the various stages of seg- 

 mentation. Smitt has- also recorded the formation of ova 

 within the ooecium. In the case just referred to, the very 

 small size and rudimentary condition of the ovum in 

 its early stages seem to show that it must have been 

 something different from the ovum developed in the cell, 

 which is perfectly formed and of considerable size when 

 it passes into the marsupium. The subject must be left 

 for future investigation. 



The direct passage of the ova into the ooecium has not 

 been witnessed ; nor have we, I believe, any observations 

 showing by what means it is effected. They are some- 



