INVEETEBBATA, CRYPTOGAMIA, MICEOSCOPY, ETC. 797 



and is placed at about the centre of the trunk-segment ; owing to its 

 projection outwards, it has by some authors been spoken of as the 

 " ventral saddle." Here again there is a fibrous medullary and a 

 cortical cellular subtsance. In addition to the commissures already 

 noticed, there are given off from it ten to twelve delicate nerves on 

 either side, and two well-developed trunks from its posterior aspect. 

 These various trunks are not distinctly separated from one another, 

 but unite largely so as to form a considerable nerve plexus. 



There appear to be considerable difficulties in the way of the 

 examination of the mesodermal portion of the nervous system. Ee- 

 turning to the two motor nerves, which are given off from the supra- 

 cesophageal ganglion, we find tliat they, after passing some way 

 forwards, make a dip into the mesoderm ; here they are enlarged into 

 a ganglion, which may be known as the lateral cephalic ganglion. 

 This body is semilunar in shape, and consists largely of dotted 

 substance and slightly of superficial cells. Several uerves are given 

 off from it, which pass to the muscles of the head. There are also on 

 either side two very small mesodermal ganglia, which are like those 

 developed on the cephalic nerves. One of these is called the buccal 

 ganglion. Certain difficulties still remain to be overcome as to the 

 innervation of the musculature of the trunk ; it seems that either the 

 numerous well-develoiied nerves which are given off from the meso- 

 dermal cephalic ganglia supply these parts, or that the superficial 

 tegumentary plexus already noticed sends fibrils to the muscles. The 

 author inclines to the former view, and points out that, if it be correct, 

 the function of the ectodermal nerve-plexus would be to convey 

 stimuli to the ventral ganglion, whence, by the commissm-es, they 

 would be carried to the supra-oesophageal ganglion, and thence con- 

 veyed by the two motor nerves to the musculature. If this view shall 

 be shown to be right, it will clearly follow that, in the Chaitognatha, 

 the sensory and motor nervous systems are distinct fx'om one another, 

 and that the former would be ectodermal, while the latter would be, 

 with the musculature, mesodermal in origin. 



There are some important points in the characters of the mus- 

 cular system. As is well knowu, the muscles of these creatures arc 

 transversely striated ; it is now further pointed out that the muscular 

 lamclla3 are set in such a way that the delicate intersjiaces between 

 them only open towards the coelom. Of the questions which we 

 ask ourselves when wo examine into the characters of this system 

 one of the most important is that which has refcrcucc to the relations 

 of the muscular elements of the Cha;tognatha to those of other animals. 

 It seems impossible to institute any comparison between tlicm and 

 either the Vcrtebrata oi- the Arthropoda, for the muscular fibrils 

 are not arranged in bundles, but in lamella) ; there is, however, a 

 very considerable x-cseniblance to what obtains in the Ccolenterata, 

 and the study of this resemblance seems to lead to the conclusion that 

 in tlie Cha;tognatha the muscle-fibrils were, primitively, spread out in 

 a tliin lamella, and that, by tlie growtli of tliis, fddiugs were formed 

 which led to the leaf-like arrangement which obtains, in some parts, 

 later on ; further considerations lead to the important conclusion that 



