Sponge-fauna of Norway. 139 



tion which converts an indifferent cell into a muscular fibre 

 consists simply of a limitation of its contractility to a parti- 

 cular direction, so that it contracts in a longitudinal and 

 broadens out in a transverse direction ; its irritability is by no 

 means suppressed ; and, as is well known, both striated and 

 unstriated muscles are capable of responding to thermal, 

 chemical, and mechanical stimuli, quite independently of any 

 nervous stimulus. This being so, all muscles, both those 

 connected and those not connected with a nervous apparatus, 

 may be regarded as neuro-muscles ; and I, for my part, do not 

 see what is to be gained by introducing this term into our 

 nomenclature ; it seems to imply that in the muscles of the 

 higher animals something, some property, has been lost 

 which was present in the muscles of such animals as are 

 without a nervous supply ; while we know this not to be the 

 case. Of course a nerve is in a very different case ; the tissue 

 which has been converted into a nerve has not only gained 

 an enhanced irritability, but has lost all trace of contractility ; 

 and if we found a nerve possessing contractility we might 

 begin to think of coining some new term to distinguish it 

 from the more highly specialized tissue. The inconvenience 

 which would attend the recognition of muscles and " neuro- 

 muscles " as distinctly different tissues may be illustrated by 

 the observation of Engelmann, who states that the middle 

 third of the ureter of the rabbit contains no discoverable ner- 

 vous structures, and yet exhibits automatic and rhythmical 

 contractions *. Surely we cannot be expected to call the 

 muscles of this part of the ureter by a different name 

 from those otherwise quite similar ones of the rest of that 

 structure. 



Whatever our opinions with regard to nomenclature may 

 be, the difficulty of explaining the manner in which the mus- 

 cular layer of our sponge receives its stimuli remains the 

 same ; it is so important a tissue of the sponge, so perfectly 

 differentiated, that one can hardly believe associated nerve- 

 structures to be absent ; and yet I have not been able to dis- 

 cover any trace of the presence of such structures. The large 

 elliptical cells underlying the muscular layer and surrounding 

 the subcortical crypts are wonderfully like ganglionic cells ; 

 but though they sometimes are elongated in one or other 

 direction into a tear-drop shape, yet they are never prolonged 

 into any distinct thread which might be regarded as a nerve. 

 They do not seem to be nerve-cells ; and perhaps they may be 

 "ova;" but without tracing their development it is impossible 



* Foster, Text-book of Physiology, 1878, p. 83. 



