446 MR. P. H. GOSSE ON THE STRUCTURE, FUNCTIONS, AND HOMOLOGIES 
have no relations of affinity with others, it is a subject of interest to inquire. What is 
the homological value of the complex apparatus we have been considering? or. What 
organ or set of organs do they represent in other classes ? 
1.31. It has been usual to compare the jaws of the Rotifera with the gastric teeth 
in the higher Crustacea, but I do not think there is in them any homology with 
these appendages. It is true that the great subcartilaginous crop in Asplanchna 
(fig. 56), a structure unparalleled by any other genus in the whole class, presents a 
curious similarity, in form and appearance, to the stomach of some of the Decapods, 
particularly that of Cancer pagurus-, but the resemblance diminishes on examina- 
tion ; and the bruising teeth of the Crab have no more analogy with the expanding 
jaws of the Asplanchna, than with the complex apparatus of the more normal Roti- 
fera. The resemblance lies in the circumstance that, in each case, the viscus con- 
sists of membranous walls, stretched, as it were, over a subcartilaginous framework, 
of a somewhat cubical shape. But the positions of the afferent and efferent orifices 
differ importantly, in the two viscera, in relation to the angles of the framework, in 
situ as well as inter se ; the pyloric orifice in the stomach of the Crab being situate 
at the extremity most remote from the cardiac, while, in the crop of the Asplanchna, 
the efferent orifice is placed close to the afferent, at the ventro-anterior angle. 
1 32. But again ; this viscus in the Crustacea is a true digestive stomach ; whereas 
the crop of Asplanchna is merely a temporary receptacle, separated from the stomach 
by a long oesophagus : as there is thus no homology between the viscera themselves, 
there can be none between their respective appendages. 
133. If the manducatory organs of the Rotifera were really represented by the 
gastric teeth of the Crustacea, the small central piece of the latter would, of course, 
be the incus of the former: but this cannot be, since the central piece of the latter is 
affixed to the dorsal wall of the viscus ; whereas, in Rotifera, the incus springs from 
the ventral or inferior side, its muscles forming the ventral lobe of the bulb. 
134. Once more; the gastric teeth are simple masses of calcareous matter, depo- 
sited, in the form of tubercles, on the interior of the parietes of the stomach, to grind 
the food as it passes through the pylorus ; whereas, the jaws of the Rotifera are 
complex organs, distinctly articulated, tied by ligaments, moved by their own proper 
muscles ; and their function is, often, to seize prey without the mouth, and always to 
bruise or lacerate it before it enters the stomach at all. 
135. Homology cannot consist with such diversities as these; and, therefore, the 
gastric teeth of the Crustacea have no true analogy with the jaws of the Rotifera. 
136. If it should be objected that, in Floscularia, &c., we find the jaws affixed to 
the walls of the digesting stomach, 1 reply, that these are the most aberrant forms of 
their class; and that we must not ground our deductions of analogy upon the con- 
dition of organs that are just vanishing, or merging into a remotely diverse type; 
especially when the comparison would tend to unite opposite ends of a series; as, in 
the present instance, the Flosculariadoe are undoubtedly the lowest forms of Rotifera, 
