ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 257 



every two pairs of mesenteries ; the septa lying in these two classes 

 of chambers are similarly called exosepta and entosepta. 



Previous observers, the chief of whom are Lacaze-Duthiers, 

 V. Koch, and Moseley, seem to have settled that : (i.) the adult madre- 

 porarian polyp is built distinctly on the Actiniau type, save when as 

 in CaryophylUa the external body-wall is absent and replaced physio- 

 logically by the imperforate theca ; (ii.) the corallum is a product of 

 the ectoderm and is deposited outside the embryo ; (iii.) this ectoderm 

 persists in the adult as the layer of calycoblasts to which the con- 

 tinual growth of the corallum is attributable ; the skeleton is thus 

 morphologically external to the polyp throughout life ; (iv.) between 

 this layer and the cavity of the coelenteron, and clothing every part of 

 the skeleton, is a layer of mesoderm and endoderm, forming the 

 internal body-wall ; (v.) septa, when present, always lie between a 

 pair of mesenteries, and sometimes also in the spaces intermediate 

 between pairs of mesenteries ; (vi.) tentacles may be exocoelic as well 

 as entocoelic, but exosepta may be present without corresponding 

 tentacles. 



Flabellum patagoniclmm has a solitary conical corallum ; the 

 anatomy is essentially that of the Actinian, except in the absence of 

 an external body-wall ; the tentacles are simple hollow evaginations 

 of the entocoeles, and are covered by small prominences, each of 

 which is a battery of nematocysts. The acontia are ejected through 

 definite openings, and these are therefore directly comparable to the 

 cinclides of Actinia. The ova are developed on all three orders of 

 mesenteries and appear to resemble those of Actinia ; as testes were 

 not seen, Flabellum may be supposed to be dioecious. The ectoderm 

 of the mouth-disc has distinctly the appearance of a secreting layer ; 

 in the stomodoeum the ectodermal cells are not modified as in the 

 siphonoglyphs of Alcyonarians. The coelenteron is lined by endoderm 

 of cubical or columnar cells ; at the point where it passes into the 

 mesenterial filament its characters change, and the histological 

 appearance bears out the physiological doctrine that the filament 

 secretes a proteolytic fluid. 



Bhodopsammia parallela is next described ; it presents very simple 

 histological characters. 



Porifera. 



Observations on Fresh-water Sponges.* — Prof. F. Vejdovsky 

 finds that Spongilla sibirica, lately described by Dr. Dybowski, is 

 identical with S. fragilis of Leidy ; the following differences are, 

 however, to be noticed ; the groups of gemmules are generally but 

 not always arranged in fours ; isolated gemmules, or groups of 2, 3, 

 or 6 are found ; the last large number seems to be very rare ; the 

 horny membrane is always visible, and not obscured as in S. fragilis. 

 The author observes that the polar air-tube in S. fragilis plays an 

 important part in the life of the gemmules, for it is in direct con- 

 nection with the upper process of the gemmule, which is generally 



* SB. K. Bohm. Gesell. Wiss. Prag, 1884 (1885) pp. 167-72 (1 pL). 

 Ser. 2— Vol. VI. S 



