on the Animal or Vegetable Nature of Sponges. 425 



gastrcs, by their multiple repetition form the segmented nutritive 

 apparatus. 



In connexion with the beautiful observations upon the deve- 

 lopment of the siliceous spicules, even in swarming spores, the 

 inquiry as to the possibility of such inception of silica from the 

 water becomes still more pressing, although in glass vessels it 

 may readily be explained from the glass. 



These siliceous spicules present another character, which this 

 is the place to mention. They have no corresponding analogy 

 in the elements of the animal body, but have a great analogy in 

 those elementary parts of plants which, as fusiform, thick-walled 

 liber-tubes, belong to the prosenchyma, and also, sometimes, like 

 the siliceousthreadsof//7/«/o7?^???«, become several feet in length. 

 These thick-walled liber-tubes of plants consist of separate short 

 cells, and, according to the most recent investigations *, some- 

 times contain milky juice in their median canal. They are va- 

 riously formed — sometimes (distinctly in Cannabis) digitated at 

 the extremities and variously united in the middle, always 

 eylindical, sometimes knotted with pore-canals. The spongo- 

 lithes are also cylindrical, also frequently divided at the ex- 

 tremities, and variously furnished with verticillate branches 

 or anchor-like t- Many are, like twin-crystals, crossed either 

 obliquely or at a right angle, like staurolith ; many are glandi- 

 form, globular, with or without conical points, comparable to 

 the frequently stellate hairs of plants (stellate hairs in the 

 interior of the stem of Nijmphccce and on the surfaces of some 

 leaves), but very rarely to animal cells; all are, therefore, 

 morpholithes in the sense ascribed by me to that term in the 

 last plate in my ' Mikrogeologie,' 1851-. Frequently the sur- 

 faces of the fusiform spicules are perforated (])ore-canals) and 

 present canals passing perpendicularly to a constantly pre- 

 sent median tube {Spongolithis foraminosa and S. fistulosa J, 

 S. porocyclia § and ^S'. porosa\\. In the Spongolithes also there 

 is never air in these tubes during life, as may be learnt from the 

 fact that under the microscope they do not appear as bhick 

 streaks, but colourless and difHcult to make out, whilst in dead 

 Spongolithes in water this blackness is distinct. AVhen alive they 

 are consequently filled with a colourless juice. Nodose Sponge- 

 Utiles also are notunconmion (S. mesogongyla^^y S.ifodosa, nodu- 

 losa'^'^% and inonite'^f, S. trac/icogoiigi/lwll and S. philippensis). 



* Sclmcht, PriifungdcrGcwebc, 1853; Milchsaftsj^efiisse, 1856. Ilans- 

 tcin in his prize essay on the '' Milchsaftsgefasse," 1 8(14. 



t Schacht, 185.'i, HaulFaser, taf. vi. fi},'. 4 b. 



X Mikrogeologie, taf. xvi. tig. 118 ss.furcnta, and fig. 119. 



§ ]\Ionatsbericht, 1861. |1 Ihid. 1845. 



1[ Mikrogeol., taf. xvii. ** Monatsbcricht, 1855, 1861. 



tt Mikrogeol. taf. xxxiv. 1% Monatsbericht, 1856. 



Ann. ^ Mag. K Hist, Ser. 3. Vol. xix. 31 



