ZOOLOGY. 481 



PORIFER. 



Sponges. 



The nervous system in sponges. — A specialized nervous system was 

 formerly deuied to the sponges, and has only been recognized within a 

 comparatively few years. The last investigator of the subject has been 

 Dr. R. von Lendenfeld. He has especially studied the muscular and 

 nervous systems in the horny sponges, especially of Australia, and has 

 formulated his conclusions and deductions therefrom. Premising that 

 there are certain structures on the distal margin of the muscular mem- 

 brane, he interprets them as follows: "The whole thickening, which 

 is interrupted only here and there, consists of ganglion-cells, the nuclei 

 of which are distinct in preparations, although their contours do not ap- 

 pear distinctly. The granular threads which are given off from these 

 ganglia in a tangential direction, are nerves which establish the con- 

 nection of the ganglia with more distant and at present still unknown 

 structures." 



From the description given, " it appears that the zone of sense cells 

 runs along the upper margin of the muscular membrane, so that two 

 bands of sense-cells are formed, bordering the tissue filling the groove 

 at the surhice." 



Dr. von Lendenfeld believes that " this structure may be directly 

 compared with the amiular nerves of cycloneural medusae (Eimer), and 

 indicates that the sponges, being capable of a development similar to 

 that of those cnidaria, were not probably so very different from them 

 as we commonly suppose. It must, indeed, be admitted," says Dr. von 

 Lendenfeld, " that, by convergent development, a resemblance may here 

 have been produced which does notjustify any jjhylogenetic conclusions, 

 especially as these structures in the sponges are mesodermal, and not 

 subepithelial as in the hydromedusce." 



In conclusion, it is said that " both the muscle and nerve cells are 

 mesodermal. The epithelia of the sponges nowhere apj^ear to be further 

 developed after the fashion of the higher coelenterata. Both endoderm 

 aud ectoderm always remain single." (A. and M. i'J'at. Hist. (5), xvii, 

 pp. 372-377.) 



CCELENTERATES. 



Polyps. 



The coral of madrepores in relation to the soft parts. — The compre- 

 hension of the relations of the hard coral to the soft parts of the awi- 

 mals which excrete it is rather difficult, and has been facilitated by Dr. 

 G. von Koch in a special memoir upon the subject. The results are. 

 summarized in the Journal of the Royal Microscopical Society. 



I. The basal plate. " This is excreted between the aboral terminal sur- 

 face of the body and the substratum to which the skeleton is attached." 

 H. Mis. 600 31 



