Chap. IV. PARYPHA CROCEA. 265 



organic shape, and the cells {Fir/. 23"-, u^ a^) are disposed in two parallel layers, 

 as in the adult (PI. XXIIP. Fig. 2, e). Individually they are cylindrical, and about 

 twice as long as thick. The remainder of the interior mass of cells («) is the 

 same as in the last stage, except that they are not so crowded. At the birth 

 of the hydroid, the cells of the outer wall (PI. XXIII. Figs. 26, 26% and 26% a) are 

 too hyaline to be visible in a natural state. The only sign of organization that we 

 have here, are the scattered lasso-cells («' cr) which give the wall a nodulated 

 appearance. At the globular tip {Fig. 26, c) of the tentacles these lasso-cells are 

 crowded so as to touch each other, and their projecting ends give the sui'foce 

 a papillate aspect, while the lasso-threads, frequently extended, render it bristling 

 here and there. The interior wall {b) is very conspicuously cellular. The cells 

 are, however, far less numerous than in the adult ; toward the base of the tentacles 

 they are the most frequent, forming at least three layers {I?) between the upper 

 and lower side, but in the vicinity of the tip there are only two layers {b). The 

 outer ends of these cells are irregularly four-sided, excepting in some instances 

 toward the base of the tentacles, where they have a strong tendency to be polygonal. 

 In a view from above {Fig. 26"), the individual cells {b) — the two ranks which lie 

 right and left — are opposite to each other, and as they are square, or at least 

 parallelogramic, the walls of their coinciding and adherent ends form a thick par- 

 tition [b"^), which has the appearance of being a solid column, running the whole 

 length of the tentacle. The contents of these cells are perfectly homogeneous 

 and hyaline. The horny sheath {Fig. 14", c), which is developed just before the 

 young escapes from its parent, is very transparent, faintly tinged with yellow, and, 

 as far as we can see, structureless. We have a suspicion, that with improved 

 lenses, a lamellar structure could be discovered. 



The Medusoid. — In the beginning of the formation of the medusoid, the cells 

 of the outer and inner walls are identical with those of the pedicel from which 

 the bud springs. These characters they retain, for the most part, throughout the 

 life of the medusoid, but there are one or two exceptions, where they undergo 

 slight modifications. In the flat, thin tentacles {Fig. 12"), those which compose the 

 inner wall (e) are enormously developed, both in length and breadth, to about 

 thrice their original diameter, and are perfectly hyaline. In a half-grown medusoid 

 a single row of them occupies about one half the height of the tentacle, and 

 form a broad border, just within the thin strip of the outer wall {d). In the 

 proboscis of a full-grown medusoid, the cells of the wall {Figs. 17, b, and IT'', b) 

 are about half again as large as the original size, but otherwise very little changed. 



VOL. IV. 34 



