1867.] DR. J. S. BOWERBANK ON HYALONEMA MIRABILE. 2/ 



of the microscope, closely resemble a beautiful and elaborately con- 

 structed Gothic crypt. In this sponge the oscula are simple ori- 

 fices, not projecting beyond the dermal membrane as in Hyalonema. 

 But the same purpose prevails in both descriptions of cloacal organ, 

 that of discharging the fsecal matters at a distance from the inhalant 

 surface of the sponges. A section of one of the feecal columns of 

 Ciocahjpta i^enicillus is represented of the natual size in the ' Philo- 

 sophical Transactions of the Royal Society of London' for 1862, 

 pi. 7'6. f. 4 ; and a magnified view of a portion of the same column 

 is represented by fig. 5 ; and also in ' Monograph of British Spon- 

 giadce,'' vol. i. pi. 30. figs. 360 and 361. 



Elongated cloacal projections from sponges are by no means un- 

 common organs. In large specimens of Jlalichondria panicea and 

 several other British species of sponges such organs are frequently 

 put forth ; but in these cases the distal extremity is always open, and 

 the production of these organs are the exception, not the rule : but 

 the contrary is the case in the British genus Polymastia, very simi- 

 lar in its skeleton-structure to Alcyoncellum, Quoy et Gaimard {Eu- 

 plectella, Owen, Trans. Zool. Soc. Loud. vol. iii. p. 203). 



In Polymastia mammiltaris (^Halichondria mammillaris, Johnston) 

 there are frequently on a single specimen from forty to fifty of these 

 cloacal organs, springing from a sponge about 2 inches in length and 

 breadth and not \ inch in thickness, but attaining 1 inch in height, 

 with a diameter of rarely more than 2 lines, the distal terminations 

 being always closed ; the minute oscula are dispersed on all parts of 

 the cloaca, as in the corresponding organ in Hyalonema. Othei* 

 British species of the same genus approach still closer to the form 

 and peculiarity of Hyalonema. In Polymastia spimda the basal 

 portion is exceedingly thin ; and the cloacal projections, seldom 

 exceeding two in number, are about an inch in length, being in 

 height at least twenty times the length of the thickness of the basal 

 sponge. 



In a third species of the same genus (P. bullosa) we have a still 

 closer approach in form to Hya.'jiiema, the basal mass of the sponge 

 being bulbous, in the form of a small onion, with a single long slender 

 cloacal tubular appendage crowning its summit, with a length rather 

 greater than the height of the bulbous mass beneath it (Monograph 

 of British Sponges, vol. ii. p. 61). The structure of the column of 

 Hyalonema, considered as a sponge, is not so anomalous as it at first 

 appears. In truth it is only one of several varieties of such cloacal 

 appendages, all of which approximate closely to each other in form. 

 In Polymastia we have the cloacal organ hollow and closed at its 

 apex, but supported by an external network of siliceous spicula, 

 with the oscula dispersed over its surface. In Euplectella aspergil- 

 lum, Owen, the skeleton is very similar to that of Polymastia, with 

 the difference of the oscula being congregated at its distal extremity. 

 In Ciocahjpta the cloacal organs closely approximate to those oi Hya- 

 lonema. Their parietes are thin, like those of Euplectella, Owen, 

 with a central axis of spicula supporting the organ in an erect posi- 

 tion J in Hyalonema the spicula composing the column are exceed- 



