28 



row, elongated, minutely granulated body, extending along the me- 

 sial line of the dorsal parietės of the body for the extent of its two 

 anteriov thirds : about -į- an inch from the head it gives off two slen- 

 der capiliary tubes, ■vvhich unite below the origins of the lateral 

 nerves, and enter the commencement of the oviduct. The com- 

 mencement of this tube, formed by the junction of the two ducts 

 just mentioned with those of the seminal vesicles, is very narrow : 

 in the greater part of its course it is coiled in numerous and complex 

 gyrations around the intestine, but towards the lower third of the 

 body its coils become fewer and more distant, the brown ova are 

 seen in scattered masses, and at length it runs parallel with the in- 

 testine straight to the anus. It is \videst at the commencement of 

 the coils ; then becomes narrower ; and afterwards continues of the 

 šame diameter to its termination. 



The cerebral ganglion mentioned by Cuvier was very conspicuous 

 in the specimen here described : it is situated between the mouth and 

 the commencement of the oviduct, and is consequently sub-oesopha- 

 geal. Eight pairs of nerves may be distinguished going from it in a 

 radiated manner. This radiated disposition of the nerv'ous system is 

 similar to that which obtains in the Slug {Limax) ; and it may also 

 be observed that the disposition of the muscular system in Limax is 

 analogous to that of Linguatula, being most developed at the sides of 

 the foot, and least along the middle line, which is thin and semi- 

 transparent when viewed against the light. If it ■vvere allowable to 

 trace further the analogy of form subsisting between genera so \yidely 

 separated, the two fossa; with their little hooks on either side the 

 mouth of Linguatula, might be compared with the two depressions, 

 "which, \vhen the tentacula are retracted, may be seen in the šame 

 situation in the head of the Slug. It is the superior organization of 

 these parts, required for its superior powers of locomotion, that ren- 

 ders necessary the further development of the nervous system in the 

 Slug ; and the completion of the cerebral ring and the development 

 of the supra-cesophageal ganglia constitute the chief difference be- 

 tvveen it and Linguatula in this part of their organization. In likę 

 manner the action of the museles in the Slug occasions "vvaste, and 

 demands a proportionate supply of new material ; and hence the ne- 

 cessity of the superaddition of a sanguineous system for the car- 

 riage of the restorative molecules, of a more complex digestive appa- 

 ratus for their supply, and of respiratory and secretory organs for the 

 elimination of the waste parts of the body. In Linguatula, on the 

 contrarj'^, the sphere of action being limited to a dark cavity, the 

 necessity for the superadded structures does not exist ; its food, al- 

 ready animalized, reąuires only a simple canal to complete its assi- 

 milation ; neither heart nor vessels are conspicuous ; and it is pro- 

 bable that nutrition is effected by transudation and imbibition. 



The reading of Mr. Owen's Paper vpas accompanied by the exhi- 

 bition of drawings in illustration of the structures described in it. 



