14 BRYOZOA ECTOPROCTA. 



embryos. Such an aperture was found in Farella by Van Beneden, 

 and in Hupojiliorella by Ehlers. 



In a few Gymnolaemata {Alcyonidium gelatinosum, Memhraiiipora 

 pilosa) Farre, Schmidt, and Hincks found a flask-shaped ciliated 

 canal [nepliridium V) connecting the body-cavity Avith the surrounding 

 medium and opening out between the tentacles. Prouho (No. 28a) 

 recently observed in some species of Alcyonidium, that this inter- 

 tentacular organ was connected with oviposition. In Alcyonidium 

 alhidum, tlie eggs probably undergo fertilisation Avithin the body- 

 cavity and become surrounded by a soft shell, being then ejected 

 into the surrounding medium through tlie intertentacular organ while 

 the parent polypide is extended, further development taking place in 

 the water. More complicated conditions are found in Alcyonidium 

 duplex. In tliis form, at the period of sexual maturity, the (male) 

 polypide of a zooecium wliich is without an intertentacular organ 

 develops spermatozoa. At the same time, on the aboral side of this 

 zooecium, a second (female) polypide, provided with an ovary and 

 an intertentacular organ, is developed ; soon after fertilisation the 

 male polypide degenerates. 



The fertilised eggs, which are provided with a shell, probably 

 reach the tentacular sheath through the intertentacular organ ; here, 

 each attached by a fine stalk, they pass through their further 

 development. AVhen the polypide is extended, the part of the 

 tentacle-sheath carrying the eggs is evaginated. In this position 

 the egg-shell bursts and the larva swims about freely. 



Within the ovaries, which originally consist of small, indifferent 

 cells, a few (2-5) young egg-cells soon appear, the remaining cells 

 becoming grouped round these to form a follicular epithelium 

 (ViGBLius). Of these young egg-cells, two at first develop more 

 than the others ; but, as a rule, only one egg becomes fully mature. 

 This egg remains at first connected witli the ovary l)y means of a 

 strand, Avliile what remains of the ovary draws back to the body-wall 

 so as to serve later as the place of origin of another egg. (On the 

 conditions of the maturation of the egg and the ooecia of the 

 Phylactolaemata, see below, p. 33.) 



Remarkable conditions of enibryogenesis were found by Hahmeu (No. 15) in 

 Crista, a form in which the rijie ovicells contain a large number of embryos.* 

 Beside these is found a protoplasmic nucleated network which sends out finger- 



* [This condition is brought about by a fission of the primary sexually- 

 produced embryos. As many as one hundred secondary embryos produced l)y 

 budding are found in a single ovicell. Hakmeu, Quart. Journ. Micro. Sci., 

 Yols. xxxiv. and xxxix. — Ed.] 



