362 REVIEWS. 



sponge is opposed by any of Dr. Bowerbank's facts, or would cause 

 any but verbal changes in his statements. We regard the channels 

 through a sponge as bearing some analogy to the central channel of a 

 colony of Pyrosomata, though exhibiting a much more complicated 

 structure. The nature and use of these channels are explained in the 

 following passage by our author : — 



"the interstitxal canals and cavities. 



" These organs exhibit their most complete mode of development in the genus 

 Spongia and in the Halichondroid sponges, occupying nearly the whole of the 

 masses of the animals. They consist of two distinct systems, an incurrent and ao 

 excurrent one. The incurrent series have their origin in the intermarginal cavi- 

 ties immediately within the dermal membrane, and their large open mouths 

 receive from these organs the water inhaled through the pores, and convey it to 

 the inmost depths of the sponge, ramifying continually like arteries as they pro- 

 ceed in their course down .van], until they terminate in numerous minute branches. 

 The inhaled fluid is then taken up by the minute commencements of the excurrent 

 series, which continually unite as they progress towards the surface of the sponge, 

 ^n the manner of veins in the higner animals, until they terminate in one or more 

 large canals which discharge their contents through the oscula of the sponge. 

 This system is found to obtain in the whole of the genus Spongia and in the 

 massive Halichondroid sponges, which have their oseula dispersed over their exter- 

 nal surfaces. By this mode of organization the inhaled fluid, laden with nutritive 

 particles, is poured at pleasure into the internal cavities of the sponge, flowing 

 over extensive membranous surfaces coated with sareode ; so that the aggregated 

 surfaces become a great system of intestinal action, fully equal in proportional ex- 

 tent to that of the intestines of the most elaborately organized mammal. 



They do not in every genus exhibit the regularity of structure described above, 

 and in some cases the canalicular form resolves itself into a series of irregularly 

 formed spaces. In other case-, where a common cloaca exists, there appears to 

 be but one system of interstitial canals, those which convey the inhaled fluid 

 from the pores through the substance of the sponge to the parietes of the great 

 central cloacal cavity which receives the whole of the fajcal streams, rendering the 

 system of excurrent canals unnecessary. 



" In the Cyathiform sponges "we find a somewhat similar structure. The outer 

 portion of the cup is essentially the inhalant surface, and the interior of it the ex- 

 halant one, and there accordingly we generally find a great number of small oscula 

 dispersed on all parts of it, very often having their margins slightly elevated, that 

 the fascal matter that issues may be discharged free of the surrounding mena- 

 hrane. 



" The large fistular projections which form such striking and beautiful objects 

 in the genus Alcyoncelhiin are also great cloacal organs, their dermal membranes 

 abounding in pores, and their inner surfaces furnished with oscular orifices, the 

 intervening space being occupied by the interstitial cavities, the intei'ior forming 

 one large cloacal cavity, which discharges its contents through a cribriform moutbi 



