BUYOZOA. lol 



generation ; the one by gemma3 or buds from the common stem or 

 polypary, which appears to be uninfluenced by season, and which in- 

 creases the size of the aggregate mass of the Bryozoon ; the other by 

 the liberation of the young, usually in the form of locomotive ciliated 

 larvae, which takes place at certain seasons, generally in spring. 



In the Flustra the gemmae are developed from the cells of the 

 pre-formed individuals ; but in those Bryozoa which have connecting 

 stems the buds arise from the stem. They are at first homogeneous ; 

 then a distinction may be observed between the cell {fig- 71, C, a) 

 and the visceral contents (b) ; afterwards the tentacles may be dis- 

 cerned, which are at first short and stumpy ; finally, the cavity, walls, 

 and divisions of the alimentary canal become distinguishable. 



In regard to the generation by locomotive larv£e, these are, doubt- 

 less, originally developed from fertile ova. 



Certain phenomena have been observed in the Bryozoa which 

 justify the belief that the individual polypes are male and female. 

 Dr. Farre has figured a specimen of the Valkeria cuscuta* ; in which 

 he observed a very remarkable agitation of particles in the visceral 

 cavity, caused by a multitude of minute cerearioids swimming about 

 with the greatest activity in the fluid with which that cavity is filled : 

 they consisted simply of a long slender filament with a rounded ex- 

 tremity, by which they occasionally fixed themselves. Similar moving 

 filaments were not unfrequently observed in other species. On one 

 occasion Dr. Farre observed them in a specimen of Halodactylus, 

 drifting rapidly to the upper part of the visceral cavity, and issuing 

 from the centre of the tentacula, indicating an external communica- 

 tion with the cavity of the body. Dr. Soulby, of Dover, informs me 

 that he distinctly saw a stream of spermatozoa escaping, like smoke, 

 from the terminal orifice of each tentaculum of a Halodactylus. The 

 analogy of these cerearioids with the spermatozoa discovered by 

 Wagner in the tortuous generative tubes of the Actinia, indicates 

 their real nature and importance in the generative economy of the 

 Bryozoa. Van Beneden has since communicated his discovery of 

 male and female polypes on the same polypary of the Alcyo7iella ; 

 the males are fewer than the females, and are recognizable by 

 the conspicuous spermatozoa, formed by a testis, which holds a 

 similar position in the male polype to that of the ovary in the female, 

 viz. behind the stomach.f 



To the same able observer w^e are indebted for illustrations of the 

 development of the impregnated ova in another genus of Bryozoon, 

 viz., Pedicellina. The ova are pyriforra, and are aggregated like 



* XXXV. pi. xxiii. fig. 5. t CXXXIV. p. 222. 



L 4 



