Chap. IV. PARYPHA CROCEA. 253 



a single, simple cavity, like that of the digestive cavity. At the neck of this 

 expansion, where it joins the cylindrical portion of the stem, the chymiferous cavity 

 loses its simjjlicity, and becomes complicated by the centripetal projection of several 

 semi-partitions (PI. XXIIP. Fig. 7, (f f/% varying in number from two or three to 

 seven or eight, according to the age of the hydroid. These partitions arise from 

 the inner wall {Fk/. 7, d cP); they are thicker than deep, and occupy more space, 

 in a lateral direction, than the spaces (J) between them. They are most numerous 

 at the top of the stem, and gradually decrease in number in a downward direction ; 

 at irregular intervals two of them anastomose, and continue as one, and so on, 

 two more and two again, till at the base of the stem the last two run into a 

 uniform, smooth, simple wall. They have a good deal of distensibility, and some- 

 times swell out so much as almost to meet in the centre of the stem. In this 

 way they transform the interspaces into nearly closed tubes ; but the centre never 

 becomes permanently occupied by a solid cellular mass, connected with the inner 

 wall by partitions, as occurs in Tubularia Couthouyi, and in T. indivisa of Europe. 

 When seen from the outside, the stem appears striped longitudinally with alter- 

 nately dark and light bands ; the dark bands are the interspaces, and the light 

 ones the semi-partitions. When light is transmitted through the stem, the reverse 

 is the effect. The inner Avail (PI. XXIIP. Figs. 4, d, 5, d, and 7, d) of the stem 

 is quite thick, esjiecially where it projects in the form of the semi-partitions 

 {F/ff. 7, ^^ ff'^), and is lined by a loose layer of brownish-red, coarse and fine, 

 granules {Fi//. 7, /). 



The outer wall (PI. XXIIP. Figs. 4, b, 5, h, and 7, h) is about two thirds as thick 

 as the inner one ; it is rendered papillate on the outer surface by the projecting 

 rounded ends of the large cells, of which it is composed. At the lower part of 

 the stem both these walls are much thinner ; in fact, the base of the stem is 

 hardly larger than at the time when the hydroid fixed itself, and the walls appear 

 to have a corresponding thickness. The horny sheath (PI. XXIII. Fig. V; PI. XXIIP. 

 Figs. 4, a, 5, a a}, and 7, a) is not so tough as that of Tubularia Couthouyi, nor 

 so thick, but is vei-y flexible, and of a light yellow, or amber color. It embraces 

 the outer wall of the hydroid, loosely, below ; but above, it thins out and clings 

 more closely, and even adheres to the globular expansion (PI. XXIII. Fig. P, d^), 

 in the guise of an excessively thin epidermis. There is no trace of this sheath 

 on the head, as may be seen on that of Coryne and Corymorpha, but it ter- 

 minates at the constriction where the latter joins the globose end of the stem. 

 At this point it has all the appearances of an epidermic secretion, and may be 

 seen to adhere closely to the curvature of the rounded ends of the cells of the 

 outer wall. 



Proles medusoidea. — There are neither radiating nor circular chymiferous tubes 



