120 HYDEOZOA. 



but it may be observed that, in portions thus detached, the sensibility 

 appears to be destroyed before the contractile power, inasmuch as, after 

 a certain time, the vibration is kept up unintermittingly in spite of such 

 contact as would previously have caused a suspension of vibratory 

 action. 



(311.) The cilia, which are placed on the longitudinal ridges, are 

 linear-lanceolate in form, flat, and not hollow. They are not webbed 

 together, and have no communication with the vessels that run beneath 

 the ciliary ridges. Each row of cilia is mounted on a transverse base,' 

 of a more solid texture and less transparent than the rest of the body . 

 The substance of this base consists of globules irregularly imbedded in 

 a homogeneous substance*. When one of the cilia of a Cydippe is cut 

 off, it has of itself no power of motion ; but if the smallest portion of the 

 substance of its base remains attached, it moves with great vivacity. 

 Hence it is concluded that the ciliary motion is effected by undulatory 

 movements of this peculiar tissue. 



(312.) In the Beroeform Acalephae, it would seem that the vital 

 principle was equally diffused throughout every part of their fragile 

 substance, which the slightest violence is sufficient to break up into 

 pieces ; indeed it is not uncommon to find the surface of the sea covered 

 with fragments of their bodies, on which the locomotive cilia may still 

 be seen in rapid action, producing, by their decomposition of the light, 

 a splendid iridescent appearance. 



(313.) The capacious cavity that occupies almost the entire length 

 of the body of the Beroe, and communicates freely with the exterior 

 through the inferior orifice, is perfectly smooth internally, and consti- 

 tutes a kind of wide pharyngeal sac, at the bottom of which is situated 

 a transverse aperture guarded by two thickened lips, the texture of 

 which is firmer than that of the rest of the body. These lips only come 

 in contact with each other near the centre of their free margins, and 

 consequently leave on each side a gaping orifice. The cavity that they 

 thus partially close is very small, and evidently corresponds with the cen- 

 tral stomach of the discophorous Medusae, and in like manner constitutes 

 a central reservoir, from whence the vascular system is derived. 



(314.) The digestive receptacle is filled with a fluid that is continually 

 in movement, and which may be seen to pass into two lateral tubes 

 that soon each divide into four branches and, arriving at the surface 

 of the body, terminate in eight longitudinal canals that convey the con- 

 tained fluid to the cilia, which latter organs, as they are in constant 

 vibration, appear to perform the functions of a respiratory apparatus. 

 From the lateral parietes of each of the eight longitudinal costal canals 

 there arise an infinite number of small vessels or transverse sinuses ; 

 these, after intercommunicating with each other, are lost in the sur- 

 rounding parenchyma*. Arrived at the margin of the wide opening 

 * Milne-Edwards, Ann. des Sei. Nat. torn, xvi., 1841. 



