88 HYDEOZOA. 



(200.) Below the tentacula the body of the polyp appears constricted, 

 marking the boundary between it and the stem ; and soon the flower- 

 like head, becoming too large to be contained in its sheath, issues 

 forth, and, expanding its tentacula, displays itself perfectly unfolded 

 (fig. 42, g, h). The ovigerous pedicles, o, hereafter to be described, are 

 developed subsequently. 



(201.) Second mode of propagation, by free gemmce. The free 

 gemmae are produced upon distinct pedicles, which in the genus Tubu- 

 laria are developed within the lower circle of tentacula. They resemble 

 numerous appendages disposed in a circle, and forming a crown around 

 the body of the polyp (fig. 42, o). These pedicles grow in the same 

 manner as the buds and the tentacula described above ; that is to say, a 

 hollow tubercle first makes its appearance, which seems to be merely an 

 extension of the external covering of the polyp. Each tubercle slowly 

 expands, and soon divides into one or more branches, which are all 

 hollow, and the same fluid that circulates in the general substance of the 

 polyp may be observed to pass into their interior (fig. 44, A'). 



(202.) At the free extremity of each of the pedicles thus formed, a 

 distinct cell is soon perceptible (fig. 43, A, B, c, ), situated immediately 

 beneath the surface, which cell is the rudiment of a new individual. 

 No nucleus has been remarked in its interior. This primitive cell may 

 be regarded as the analogue of the vitelline sac, or, perhaps, as the 

 vesicle of Purkinje or of Wagner ; most probably, however, it is the 

 vitelline vesicle, from the circumstance that it becomes organized inter- 

 nally, in which case the reproductive process assumes the third or the 

 fourth form, subsequently to be noticed ; or else it serves for the point of 

 departure, or, it might almost be said, the mould for the formation of a 

 free gemma, which becomes organized around it at the expense of the 

 pedicle itself. It is, in effect, a part of the reproductive appendage that 

 will subsequently become detached ; but at this period of its development 

 it is impossible to determine after which of the four modes of reproduc- 

 tion the embryo will be formed. The vesicle (fig. 43, A, B, c, a) now 

 increases rapidly in size, and beneath it another membrane (fig. 43, A, 

 B, c, 6) is soon perceptible, which by its inner surface is in contact with 

 the circulating fluid. This membrane is the origin of ttje new indi- 

 vidual ; or, in other words, it is a blastoderm, formed by the internal 

 skin, and not by the vitellus. Soon there is seen, projecting from its 

 centre, a little cone (fig. 43, B, b) which, compressing the vesicle, a, forms 

 a depression upon its inferior surface, so that the vesicle begins to 

 assume the appearance of a serous membrane, yielding to the pressure 

 of the organs over which it spreads, and which it ultimately covers 

 much in the same way as the pleura covers the lungs. The tubercle, b, 

 will afterwards form the walls of the digestive cavity of the new animal, 

 and may be seen to have a circulating fluid, derived from the body of the 

 polyp, moving in its substance. Around the base of the cone, 6, may 



