286 HYDROID/E. Part IV. 



Bougainvillia, though it is a Uttle more slender, and has a more graceful aspect 

 (PI. XXVII. Fif). 10), on account of the greater length of its pedicels. It is also 

 more strongly ringed throughout, and possesses eight or ten more tentacles, twenty- 

 eight in all {Fig. 11), and tapering in form. The principal feature which distinguishes 

 this hydra from that of Bougainvillia, is its long, simple proboscis {Fig». 10 and 11, p), 

 in compai'ison with which the hydra of Bougainvillia (PI. XXVII. Fig. 3) may be 

 said to have none at all. The proboscis has all the tlexibility and plasticity of 

 that of the Camj^anularians, so often referred to by authors, and resembles it not 

 only in form but also in the absence of tentacles around the oral apertures. The 

 coronal tentacles agree also with those of the Campanularians in their occasional 

 alternate depression and elevation. When the animal is in a quiescent state, the 

 proboscis often assumes an elongate, pear-shaped form {^Figs. 10, B C, and 11, />) ; 

 but when seai'ching for food it expands into the form of a trumpet {Fig. 13, p), 

 with more or less dilated lips. 



From May to September the heads are loaded witli medusoid progeny {Figs. 10, 

 12, and 13, mil), arranged in an irregular cii'cle, just below, and parallel to, the 

 tentacles. During this season this hydra may be distinguished from the very 

 similar hydra of No. II., l)y its medusEe-bnds^ which are arranged in a moniliform 

 series, attached to each other by twos or threes, end to end {Figs. 18 and 19, 

 A B C), while No. II. 2)roduces single, scattered medusas-buds. Unfortunately, we 

 have never seen the meduste with eggs; but, judging from the females of another 

 species of this genus, figured by Dr. Wright in the Edinburgh New Philosophical 

 Journal, Vol. IX. 1859, PI. II. Fig. 2, «, and described at page 108. they are not 

 moniliform but single. The structure of the medusa will be described in the next 

 paragraph, along with its embryology. 



Proles medusoidea (PI. XXVII. Figs. 12-19). — Like all Hydro-medusoe, the bud- 

 ding embryo commences as a protrusion of the two walls of the body of the 

 hydra {Fig. 14, a h), in the form of a hernia, into which tlie digestive cavity {c) 

 projects. This continues to increase, until it has assumed a pear-shaped form 

 {Fig. 15), and has a breadth equal to the thickness of the stem of the hydra 

 (see Fig. 12, ind). At this age the cells of the outer wall {Fig. 15, a), which 

 in the hydra are so exceedingly indistinct, and barely recognizable in the initiatory 

 state of the medusa {Fig. 14), are xevy conspicuous, and, in fact, are the first to 

 attract the eye, by their beauty and remai'kable appearance. They form a single 

 layer, and have a polygonal outliiie when seen from the outer end ; in jirofile, 

 they have a broad and short, cylindrical shape, with rounded exterior ends. Each 

 cell contains a few granules, which are grouped around its centre. The inner 

 wall {Fig. 15, h), which is about twice as thick as the outer one, is lined by 

 reddish, or, rather, pink granules. Soon after this date, the outer and inner wall 



