THALASSICOLLA. 29 



original, it attaches itself to a proper object, and, losing the now useless 

 locomotive cilia, it becomes fixed and motionless, and developes within 

 its substance the skeleton peculiar to its species, exhibiting by degrees 

 the form of the individual from which it sprung. It is curious to 

 observe the remarkable exception which sponges exhibit to the usual 

 phenomena witnessed in the reproduction of animals, the object of 

 which is evident, as the result is admirable. The parent sponge, de- 

 prived of all power of movement, would obviously be incapable of 

 dispersing to a distance the numerous progeny that it furnishes ; they 

 must inevitably have accumulated in the immediate vicinity of their 

 place of birth, without the possibility of their distribution to other lo- 

 calities. The seeds of vegetables, sometimes winged and plumed for 

 the purpose, are blown about by the winds, or transported by various 

 agencies to distant places ; but in the present instance, the still waters 

 in which sponges grow would not have served to transport their pro- 

 geny elsewhere, and germs so soft and delicate could hardly be removed 

 by other creatures. Instead therefore of being helpless at their birth, 

 the young sponges can, by means of their cilia, row themselves about 

 at pleasure, and enjoy for a period powers of locomotion denied to their 

 adult state. 



(62.) Very widely distributed through the ocean, whether in tropical 

 or extra-tropical climates, peculiar gelatinous bodies may be found float- 

 ing upon the surface of the water ; indeed they are occasionally among 

 the most constant of all the various products of the towing-net. The 

 THALASSICOLLA* (for so these simple organisms are designated by Professor 

 Huxley f) is found in transparent, colourless, gelatinous masses of very 

 various form elliptically elongated, hourglass-shaped, contracted in 

 several places, or spherical, varying in size from an inch in length down- 

 wards, showing no evidence of contractility nor any power of locomo- 

 tion, but floating passively on the surface of the water. Of such bodies 

 there appear to be two very distinct kinds. In one, the mass consists of 

 a thick gelatinous crust containing a large cavity. The crust is struc- 

 tureless ; but towards its inner surface minute spherical, spheroidal, or 

 oval bodies are imbedded (fig. 14, 2), each of which appears to be a cell 

 with a thin but dense membrane, and containing a clear fatty-looking 

 nucleus surrounded by granules, the whole substance, in fact, resembling 

 an animal Palmella. Very commonly the central part of each mass, 

 instead of containing a single large cavity, consists of an aggregation of 

 clear, closely appressed spaces resembling vacuoles (fig. 14, 3) ; and fre- 

 quently each cell is surrounded by a zone of peculiar crystals, somewhat 

 like the stellate spicula of a sponge, consisting of short cylinders, from 

 each end of which three or four conical spines radiate, each of these 

 again bearing small lateral processes (fig. 14, 4 & 5). Frequently the 



* QaXaaea, the sea; jcoXXa, glue. 



t Vide Ann. and Mag. of Nat. Hist. ser. 2. vol. riii. p. 433. 



