392 POLYZOA HYPPOCREPIA. 



cous appearance, and is more or less apparently porous. The mass 

 is composed of subcylindrical tubes rising from the base to the 

 surface, nearly parallel, connected by, or permeating, a transparent 

 firm jelly-like substance, with which the tubes appear to be also 

 partially filled. The tubes are simple or unbranched, and open 

 outwardly by a roundish or pentagonal aperture, which is closed by 

 a thin membranous cover. The walls of the tubes are of the same 

 thin membranous character, pellucid, colourless, or tinted with green, 

 and without any visible vessels; they contain innumerable lenticular 

 ova of a dark brown colour, about half a line in their longest dia- 

 meter, very hard and incompressible, but in drying the centre 

 becomes depressed and more transparent than the edges. These 

 singular ova are quite smooth,* and arranged in rows in the tubes, 

 though not very regularly ; they are more abundant near the surface 

 than at the base of the polypidom, and exist in such amazing num- 

 bers as to excite surprise at the seeming productiveness of an animal 

 which appears to be very partially diffused, and is very capricious in 

 its appearance even in ponds favourable for its growth, swarming 

 in one season, of rare occurrence in the next, and perhaps then 

 for years lying dormant, until some undiscovered cause hatches the 

 egg and renews its pristine fertility. When freed from the mass, 

 the greater number of the ova swim on the surface of the water, but 

 some sink to the bottom. 



To this description, derived from specimens in a recent, but not 

 living condition, sent me by Mr. Embleton, I add the following 

 particulars derived from Mr. Teale's valuable paper. A good idea 

 of the polype will be obtained by reference to figures 5, 6, of Plate 

 Ixxiv, which are reduced copies of Raspail's. It is organically con- 

 nected with the mass, the tube forming its tunic, from which the 

 animated body issues by a process of evolution, similar to that which 

 developes the horn of a snail. When developed, the head projects a 

 short way, and is crowned with a " beautiful expansion of tentacula, 

 about fifty in number, arranged in an unbroken circle, which is, 

 however, depressed into a deep concavity on one of its sides, so as to 

 produce the appearance of a double row of tentacula in a horse-shoe 

 form. About one thousand six hundred polypes are situated on a 

 square inch of surface of the mass, consequently the number of 



M. Meyen says, on the contrary, that the envelope of the ovum is covered with 

 very fine vibratile cilia. Bull, des Sciences Nat. xviii. 313. Has not Meyen mistaken 

 the ova or seeds of the Spongilla for those of the Alcyonella ? for undoubtedly the ova 

 of the latter are smooth. 



