FORMATION OF THE EGG. 13 



I. Formation of the Egg, Fertilisation, Position of the 

 Embryo. 



The genital products of the Ectoproctous Bryozoa arise in cell- 

 masses which originate as growths of the mesodermal parenchy- 

 matous tissue (marine Ectoprocta), or of the peritoneal epithelium 

 corresponding to the latter (Phylactolaemata), on the inner side of 

 the body-wall (endocyst), or else in strands of the so-called funicular 

 tissue. The ovaries are very generally found on the neural wall 

 (dorsal side) in the anterior or middle part of the body; the testes 

 lie at the base of the zooecium (i.e., in the proximal part). In 

 the fresh-water Bryozoa, the genital rudiment frequently bears a 

 relationship to that part of the mesenterial strand which is known 

 as the funiculus. In Paludicella, for instance, the eggs lie on the 

 body-wall near the point of insertion of the upper funiculus, while 

 the spermatozoa arise on the basal portion of the lower funiculus. 

 In the Phylactolaemata, on the contrary, the ovary lies on the 

 oral body-wall, while the spermatozoa, as a rule, develop in aciniform 

 masses at the upper part of the funiculus. In Cristatella, the 

 spermatozoa arise on the mesodermal septa of the body-cavity. 



The genital products pass into the body-cavity, where, in some 

 forms, fertilisation takes place. Since the Bryozoa are, as a rule, 

 hermaphrodite, and as it is difficult to state in what way foreign 

 spermatozoa can reach the body-cavity, self -fertilisation has been 

 assumed to occur. The fertilised eggs either pass through the 

 whole of their embryonic development, up to the time when the 

 ciliated larva is formed, within the body-cavity of the parent, or else, 

 through the dehiscence of the body-wall, reach the tentacle-sheath 

 (Valkeria, Joliet, No. 17; Lepralia and Vesicularia, Ostroumoff, 

 No. 26), in the cavity of which they pass through the embryonic 

 stages till the larva hatches, or else the eggs (as in many Chilo- 

 stomata) are received into special outgrowths of the zooecium which 

 serve as brood-cavities. These are the ooecia and ovicells which have 

 been described as individuals of the polymorphous Bryozoan stock 

 peculiarly metamorphosed for the care of the brood. * 



In those cases in which the larvae pass through their earliest 

 ontogenetic stages in the body-cavity of the mother, they escape 

 either through the aperture of the zooecium, after the polypide to 

 which they belong has undergone degeneration, or else there is a 

 special aperture near the base of the tentacles for the passage of the 



* [In some Cyclostomata (Crista) the ovicells are undoubtedly modified zooecia 

 in which the polypide is rudimentary or degenerate. — Ed.] 



