50 On Parasitic Polypes and Thread-cells in Sponges. 



in by the monociliated bodies which, in juxtaposition, line the 

 interior and, projecting their cilia inwards, keep up a rapid 

 undulating vibration towards the centre of this hollow sphere. 

 The undigested parts of their food may be seen to pass into the 

 excretory canals, and, through them, to be finally ejected at the 

 vents on the surface; but whether it passes through their 

 bodies after the manner of Amosba, or has a distinct channel 

 appropriated for this purpose, has yet to be determined. 



Parasitic Polypes and Thread-cells in the Parenchyma of a 



Sponge. 



In a specimen, about two inches long, of a thick digito- 

 lobulate branched Ueniera^ tubulate, opening by a large vent 

 at the end of each lobe, and having one form of spicule only, 

 viz. thin, curved, acerate, said to be of a " pale red colour 

 when alive," and found in " Bon Bay," in " 25-65 faths.," 

 just sent to me by Prof. Wyville Thomson, I have found the 

 parenchyma interiorly to be charged with thread-cells of an 

 ovoid form, almost elliptical, and averaging 3-6000ths of an 

 inch long by 2-6000ths of an inch broad — in short, very 

 similar to, if not exactly like, that delineated by Dr. T. Elmer 

 (Schultze's Archiv fur mikroscop. Anatom. vol. iii. pt. 2, 

 fig. 1, A, p. 283). 



Not having found these cells in the dermal part of this 

 sponge, nor in the surface-layer of the great tubular vents, 

 analogous to their position in the poly})es &c., but, on the 

 contrary, in the interior of the parenchymatous structure of 

 the sponge, I began to think that they could not belong to it ; 

 so I placed a portion in water and examined it with one-inch 

 focus, when they were observed to come from minute delicate 

 polypes, seated in dilated cavities, apparently of the excretory 

 canals, the disk or head of each polype averaging 100th of an 

 inch in diameter, and supported on a short neck, which ended 

 in a little saccular prolongation that was sunk into the paren- 

 chyma or sarcode of the sponge, and charged, in its walls 

 as wel? as tentacles, with thread-cells so numerous that they 

 appeared to exceed in bulk the rest of the polype, as may be 

 seen by picking out one on the point of a needle, and putting 

 it under a higher power. 



This is the first instance, I think, in which a parasitic 

 polype has been discovered in the interior of the substance of 

 a sponge ; and when it is remembered that a microscopic 

 power with delicate manipulation under water is required for 

 their detection, it may perhaps be assumed that this is how 

 these polypes escaped Dr. Eimer's notice, and may also explain 



