Repi'oductive System of Sertularian Zoophytes. 387 



pith or fleshy axis *. They have been termed expansions of the 

 stem f. Some have considered them female individuals % or 

 polj^es of a diiferent kind from the rest, inclosed in a larger 

 cell §, and by some the vague term of ovariform buds has been 

 applied to them||. 



Now if the parallel we have drawn so far between the plant 

 and the zoophyte be carried out, these so-called " ovigerous 

 vesicles^-' should be essentially either single indi\aduals idealbj 

 metamorphosed into reproductive organs comparable to the mo- 

 uocarpous germens of plants, or a series of individuals joined to- 

 gether and merged into each other in such a manner as to pre- 

 sent the appearance of a unique body in which the ova are pro- 

 duced — comparable to sjucarpous germens among vegetables. 

 That such is the true view of their natm'e — however transcen- 

 dental it may at tu'st sight appear — I have convinced myself, and 

 hope to prove it to the satisfaction of others by an analysis of the 

 several forms of polype-vesicle presented in the family of Sertu- 

 hiriadce. 



All the ' ovigerous vesicles^ with which I am acquainted may be 

 distributed under six heads or kinds : — 



1st. ]\Iorc or less lengthened pod-like bodies, ornamented 

 with ribs and presenting a very complex aspect, such as we see 

 in several species of Plinnularia, as the British Plumularia 

 cristata and the two species figm-ed fi'om Algoa bay. This is in 

 reahty the simplest and most easily understood form of vesicle, 

 the form which has imdergone least transformation, and which 

 affords the readiest clue to the nature of these bodies. This pod 

 is nothing more than a branch, the axis of which is usually 

 shortened. In a remarkable species which I owe to the liberality 

 of Mr. Bowerbank it retains its full dimensions. The pinnse are 

 tm'ned in and united at their extremities, and webbed together by 

 the transformed and expanded walls of the polype-cells. The pod 

 has a ventral suture and a dorsal rib ; the ventral suture corre- 

 sponding to the line of junction of the extremities of the pinna?, 

 and the dorsal rib corresponding to the dorsal rib of the branch 

 and identical in structure. The lateral ribs are the ribs of the 

 pinnae, and spring from the dorsal rib alternately, exactly as the 

 pinnae do from the unchanged branches. So slight is the change 

 in this form of vesicle, that it is astonishing the contemplation 

 of it (for it has been frequently carefully figm-ed and described) 

 had not opened the eyes of naturalists long ago to the true na- 

 ture of these curious bodies. 



2nd. Ovate or round berry-like bodies, studded with spinous 

 processes more or less regularly whorled, such as we see in Thoa 

 muricata. Bearing in mind the normal spiral arrangement of the 



* Johnston, Grant. \ Carpenter. :|: Ehrenberg, Loven. 



§ Carpenter. j] Blainville. 



2D2 



