112 THE OCEANIC HYDROZOA. 



fibrous and an internal circularly fibrous muscular coat ; and he says that a " cavity occupies 

 their whole length," and opens at its base into a vessel. 



Vogt (p. 22), in describing the same species, says, " these tentacles are hollow cylinders, 



completely closed at their extremities One might regard them as very strong, thick, 



and muscular tubes, whose interior is filled by a transparent liquid, which doubtless plays a 

 certain part in the process of elongation of these organs. The principal muscular fibres 

 which form this tube seem to be disposed in ogives, so as to present the summit of the 

 ogive towards the interior of the tube. Other bundles are distinguishable which run 

 circularly, while still others are disposed longitudinally. Some of these bundles traverse the 

 interior tube in such a way as to simulate a cellular structure, which does not appear to me 

 really to exist." From this description I am inclined to believe that the structure of the 

 tentacles in the Mediterranean species is in reality similar to what I have observed. 



Vogt (p. 22) describes a peculiar glandular structure in the margin of the limb of the 

 horizontal disc of Velella spirans in the following terms : " I have already frequently mentioned 

 the clear blue line which runs along the edge of the limb. On microscopic examination it is 

 seen that this is composed of a simple series of great glandular sacs arranged side by 

 side, whose circular apertures are all situated on the dorsal face of the limb, and which 

 secrete a transparent and viscous mucus. The structure of these glandular sacs is very 

 curious, for they are wholly made up of great cylindrical cells, disposed in a radiating manner, 

 so that the fi-ee and rounded extremities of the cells are turned towards the centre of the 

 sac, whilst the other extremity is fitted into its wall. On the edge of the latter the rounded 

 contour of the cells intended to replace the cylindrical cells (of which there are apparently 



many series) is visible The inferior face of the limb is covered only by the ordinary 



integument, and exhibits the bottom of those glandular sacs, which here have no aperture." 

 Kolliker (p. 60) would seem to have observed these glands, and similar ones in Porpita, and 

 Leuckart (' Z. N. K.,' p. 115) confirms Vogt's discovery in Velella. 



The smaller polypites, or gonoblastidia (fig. 4), as they might, perhaps, be more correctly 

 termed, are supported upon longish, slender, peduncles. Their apical ends are very variable 

 in shape, sometimes wide and trumpet-shaped, with everted lips, sometimes contracted and 

 plaited. The wall of the polypite^ is, as usual, composed of a distinct ectoderm and 

 endoderm ; the former being provided with villous elevations on its inner surface." The 

 outer surface of the ectoderm also presents many rounded elevations, each of which contains 

 a great number of spherical thread-cells.' 



The wall of the peduncle has the same composition as that of the polypite itself. 



^ Kolliker (p. 53), however, states that he has seeu no hepatic striee or glandular cavities in the 

 walls of the small polypes. 



' Vogt has ohserved the two membranes of which the wall of these buds is composed, but 

 imagines that the endoderm is a structure peculiar to them (p. 27), whereas it is continuous with the 

 endoderm of the polypite. As T have stated above, these buds were discovered by Delle Chiaje, and 

 have since been observed by HoUard (who entirely mistook their nature), Leuckart, Kolliker, and all 

 the later investigators. 



' Half digested Crustacea, &c., have been observed in these organs by Lesson, Vogt, and Kolliker, 

 so that there is no doubt as to their function. 



