ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 34 



in the circular dorsal canal, or in the tubular pouch surroundinf» the 

 hydrophoral canal ; this pouch serves as a means of communication 

 between the dorsal and ventral circular canals, and is really nothing 

 more than one of the spaces formed by the peri toneal membrane, and 

 enlarged ; but neither it nor the dorsal canal have anything to do 

 with the excretory apparatus of the generative system. 



Coelenterata. 



Clavularia prolifera.* — After a description of this new Alcyon- 

 arian, G. v. Koch discusses the mode of connection of the buds with the 

 trunk ; he points out that it is a remarkable fact that these buds are 

 not mere outpushings of the body-wall of the mother-polyps, but that 

 at the base of each bud there is a canalicular network in the thickened 

 connective substance of the mother, by which the two polyp- cavities 

 indirectly communicate with one another. Discussing the question 

 of its origin," the author shows that, if it is secondary, or- if, in other 

 words, the young polyp first developes as a simple evagination, and 

 gives rise to the plexus by a partial fusion of the intermediate sub- 

 stance, it would be a structure which owed its existence to adapta- 

 tion, or had only a physiological significance, such as might be 

 explained as due to the more or less complete isolation of the polyps. 

 On the other hand, if it is primary, or, if it gave rise to the young 

 bud, then we should have to seek its morphological significance, and 

 might compare this canalicular network with the nutrient canals of 

 the Gorgonida. 



This important question could not be decided on the preserved 

 specimen which the author has- examined, but a study of some allied 

 forms shows that in this group of corals the digestive cavities of 

 the buds never open directly into that of the mother, and that 

 there are a series of intermediate stages from those in which the 

 polyp-buds are derived from simple stolons, and those in which the 

 stolons form canals in the thickened mesoderm, and those, lastly, 

 in which the thin partition between the bud and the mother is per- 

 forated by small orifices. We may therefore conclude that the more 

 or less incomplete separation seen in the Alcyonaria has a certain use, 

 and that it is not an adaptive arrangement, but one which may be 

 referred to the formation of the stolons ; the canalicular network in 

 the mesoderm of the mother-polyps, which lies at the base of the 

 buds and connects them with the mother, is a stolon-formation (in 

 its widest sense). And, further, we find that in the Alcyonaria 

 asexual reproduction is never effected by division or direct gemma- 

 tion, but always indirectly, or by stolons or structui-es homologous 

 therewith. 



A study of the new species throws some light on the horny sheaths 

 of the spicules, and their relations to the ectoderm, for we find 

 that the younger spicules are always invested in a protoplasmic 

 nucleated sheath, which may also be frequently made out in older 

 examples, where we find cells connected by pairs and having within 



* Morph. Jabrbuch, vii. (1881) pp. 467-87 (2 pis.). 



