142 Zoological Society. 



and would have been introduced under that head but for the sake of 

 convenieucy in illustrating the vertebrate skeleton. 



1 . In the Crustaceans the jaws differ in scarcely any other cha- 

 racter than size from the true legs used in locomotion. 



2. In the Myriapoda the members of the basilar segments of the 

 head are jointed and retain the form of true legs, but are used for 

 prehension (Newport in Todd's Cyclopaedia). 



3. In Insects the tarsal joints of the cranial legs are undeveloped ; 

 the femur and coxa are small or confluent with the under side of the 

 segment, whilst the tibiae are alone enormously enlarged, and thus 

 become elements in the complex mouth of Insects ; their muscles, 

 however, being attached to the basilar and posterior lateral parts of 

 the head, just as if they still subserved the purposes of locomotion 

 (idem) . 



4. All the parts of the complex mouth of Insects are thus referable 

 to the segments of the head. In the Great Water Beetle this is 

 clearly shown ; the manducatory organs visibly resemble the proper 

 organs of locomotion, and are articulated to the distinct segments 

 (idem) . 



5. We must remark intermediate normal conditions between the 

 true locomotive and manducatory form of leg ; as in the genus Onitis, 

 where the prothoracic legs are without tarsi, and the tibiae are termi- 

 nated by sharp hooks ; and in the Bubos bison, a species of a neigh- 

 bouring genus, where the tibiae strongly approach in form the proper 

 mandibles of the head : also, 



6. A monstrous condition in a specimen of Geotrupes stercora- 

 rius, where the prothoracic legs were arrested in development and the 

 tarsi were absent, so that they very closely resembled the form of the 

 mandibles (idem). 



Section III. 



The spinal cord of the Vertebrata is homologous with the gan- 

 glionic cord of the Articulata. 



1. The elements of the systems are alike, being in both cases 

 cellular nervous matter and commissural fibres. 



2. The experiments and investigations of recent physiologists have 

 proved the real independence of the segments of the cord contained 

 in each vertebra, insomuch as each performs separately from the 

 others its own reflex actions, just as is the case in the ganglionic cord 

 of the Articulata ; so that, as far as its reflex actions are concerned, 

 the cellular or dynamic element of the spuial cord is not one organ 

 or centre, but a series of independent organs or centres, as is seen in 

 the Insects, the external longitudinal fibres servuig only as commis- 

 sural or communicating portions. 



3. Those ganglia of the Insects which are perfectly separate in the 

 larval condition often exhibit a tendency to fusion in the perfect con- 

 tUtion (Blanchard iit anted). Thus in the Coleoptera the last abdo- 

 minal ganglion is always formed by a fusion of several original ones ; 

 the first and second abdominal often form a single mass with the 

 metathoracic, whilst in the Chafer this last is united wdth the meso- 

 thoracic (idem). In like manner the fourth and fifth segments in 



