REPRODUCTION OF LAGUNCULA. 495 



the bodies of the animals themselves, which is what always hap- 

 pens when the cells are in mutual apposition ; or from the con- 

 necting stem or stolon, where the cells are detached from each 

 other, as in Laguncula. There is first seen a hud-like protube- 

 rance of the horny external integument, into which the soft 

 membranous lining prolongs itself; the cavity thus formed, how- 

 ever, is not to become (as in Hydra and its allies) the stomach of 

 the new zooid ; but it constitutes the chamber surrounding the 

 digestive viscera, which organs have their origin in a thickening 

 of the lining membrane, that projects from one side of the cavity 

 into its interior, and gradually shapes itself into the alimentary 

 canal with its tentacular appendages. Of the production of 

 gemmae from the zooids themselves, the best examples are fur- 

 nished by the Flustrce and their allies. From a single cell of a 

 Flustra, five such buds may be sent off, which develope them- 

 selves into new zooids around it ; and these, in their turn, pro- 

 duce buds from their unattached margins, so as rapidly to aug- 

 ment the number of cells to a very large amount. To this 

 extension there seems no definite limit; and it often happens 

 that the cells in the central portion of the leaf-like expansion ot 

 a Flustra are devoid of contents and have lost their vitality, whilst 

 the edges are in a state of active growth. Independently of their 

 propagation by gemmation, the Polyzoa have a true sexual gene- 

 ration ; the sexes, however, being usually, if not invariably, 

 united in the same individuals. The sperm-cells are developed 

 in a glandular body, the testicle m, which lies beneath the base 

 of the stomach; when mature, they rupture, and set free the 

 spermatozoa q q, which swim freely in the liquid of the visceral 

 cavity. The ova, on the other hand, are formed in an ovarium n, 

 which is lodged in the membrane lining the tegumentary sheath, 

 near its outlet ; the ova, having escaped from this into the visce- 

 ral cavity, as at o, are fertilized by the spermatozoa which they 

 there meet with; and are finally discharged by an outlet at p, 

 beneath the tentacular circle. 



327. These creatures possess a considerable number of muscles, 

 by which their bodies may be projected from their sheaths or 

 drawn within them ; of these muscles, r, s, t, u, v, w, x, the direc- 

 tion and points of attachment sufiiciently indicate the uses ; they 

 are for the most part retractors, serving to draw in and double up 

 the body, to fold together the circle of tentacula, and to close the 

 aperture of the sheath, when the animal has been completely 

 withdrawn into its interior. The projection and expansion of 

 the animal, on the contrary, appear to be chiefly accomplished 

 by a general pressure upon the sheath, which will tend to force 

 out all that can be expelled from it. The tentacula themselves 

 are furnished with distinct muscular fibres, by which their sepa- 

 rate movements seem to be governed ; the arrangement of these 

 is seen at d. At the base of the tentacular circle, just above the 

 anal orifice, is a small body (seen at a, a), which is a nervous 



