INTRODUCTION. XCV 



tions of Metschnikoff* and Nitschef on the Freshwater 

 Polyzoa ; whilst Joliet has recently detected the same or 

 a strictly analogous arrangement in some of the marine 

 species J. I shall give a brief account of it (after this 

 writer), as it exists in the latter. In cells of Valkeria 

 from which the polypide has disappeared (being replaced 

 by a "brown body"), a mature ovum is met with at cer- 

 tain seasons, not yet fertilized, and, as it seems, hope- 

 lessly imprisoned in the closed cavity of the zocecium. 

 But at the moment when escape appears least likely, a 

 bud makes its appearance at a certain point on the cell- 

 wall (in connexion with some offshoot of the funiculus), 

 which is rapidly developed into a young polypide. The 

 latter passes to the top of the cell and develops new 

 parieto-vaginal muscles and two great retractors, but 

 otherwise remains in a perfectly rudimentary condition. 

 It is to be imagined now as being in connexion with the 

 tentacular sheath and, through the funiculus, with the 

 ovum. 



The funiculus shortens, and the sheath is proportion- 

 ately elongated ; and the polypide is thus brought into 

 contact with the egg : in a short time (but by what pre- 

 cise means is unknown) the latter makes its way within 

 the tentacular sheath, and occupies a place above the 

 polypide. The latter dwindles away and becomes a mere 

 platform (movable by means of its attached muscles), on 

 which the ovum rests, inclosed by the walls of the sheath. 

 It is now in free communication with the water ; and at 



* Bull, de 1'Acad. de St. Petersbourg, XT. (1871), p. 607. 



t Zeitsch. f. wiaaenach. Zool. xxii. 



J Op. tit. p. 70. This author seems to haYe been unaware of Metschni- 

 kofTs previous observation*. He lias noticed the "auxiliary polypide" in 

 three Ctenostomatous species, Falkfria wro form ciacuta, Bovxrbankia 

 imbricata, and LagtntUa rrpens. 



