MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 501 



mesenteries disappear, so do the corresponding septal invaginations; the metacnemes disappear 

 tirst in unilateral pairs, the protocnemes in bilateral pairs. In the anterior part of the section is 

 seen the beginning of another polyp. 



Two somewhat older buds sectionized presented the following conditions: In one only ten 

 pairs of mesenteries were de\ eloped, five complete and five incomplete, in regular alternation; in 

 the other eleven pairs occurred, six complete and five incomplete. 



The results thus briefly indicated may be summarized: 



(1) The polyps of Sob nostra a, produced asexually by gemmation, pass through the Ed/wardsicir 

 stage of mesenterial development, in which four pairs of the protocnemes are complete and two 

 pairs incomplete, just as in larval polyps. 



(2) The metacnemes begin to make their appearance before this stage is passed over, that is, 

 before the union of the fifth and sixth pairs of protocnemes with the stomodsBum takes place. 



(3) The tirst metacnemes appear along- the polypal wall, at about the level of the inner termi- 

 nation of the stomodseum, as isocnemic pairs within the dorsal or sulcular primary exocoeles, but 

 in one case within the median lateral exocoeles. 



(i) In relation to the colony as a whole the dorsal or sulcular side is inner (axial), and the 

 ventral or sulcar outer (abaxial). The succession of the metacnemes is therefore dorso-ventral, 

 antero-posterior, or from the axial to the abaxial side of the bud. 



(5) The mesenterial filaments and mesenteries disappear below inversely as the order of their 

 development: first, the metacnemes in unilateral pairs, then the protocnemes in bilateral pairs. 



(6) In the same transverse section the growth on one side of a polyp may be slightly in 

 advance of the growth on the other side. 



(7) The metasepta and metatentacles, both entoecelic and exocoelic, arise practically pari 

 passu with the mesenteries. 



BUDDING IN CLADOCORA. 



The young buds in Cladocora arbuscula generally occur singly toward the upper part of the 

 column wall of the terminal polyp of the sub-colonies. What seems to be discal budding has also 

 been found to take place, when both the parent and daughter polyps are surrounded by a con- 

 tinuous system of tentacles and a single column wall; but the extratentacular buds seem rarely to 

 arise above the level of the corallite. The reproductive power of any polyp is very limited, for 

 as a rule not more than three or four polyps are connected in a sub-colony, and among these is 

 rarely more than one immature example. Each polyp in its turn may give rise to buds, either 

 before or after becoming distinct from the rest of the sub-colony. At a very early stage the 

 growth of the lower abaxial aspect of the bud is in advance of the upper or axial aspect, thus 

 giving rise to the obliquity of the polyps to one another. 



Numerous extratentacular buds of slightly different sizes have been studied, and in most 

 specimens eight complete and four incomplete mesenteries are already present, their arrangement 

 and musculature agreeing with that of the protocnemes in Iarvse of the same stage. In one 

 case the fifth and sixth developmental pairs were absent, and. following the sections downward, 

 only four mesenteries were present a short distance below the stomodamm; then two of these 

 disappeared; the two remaining, which represented the first developmental pair of mesenteries, 

 were continued much farther, and bore mesenterial filaments almost to their termination. At 

 this early stage none of the mesenteries were in any way connected with the extrathecal continu- 

 ations of the mesenteries of the parent polyp, so that evidently the buds arise on the column 

 wall quite independently of any of the other organs of the parent, as happens in Madrepora, and 

 as appears to be also the case in Solenastrsea. 



PI. VIII, fig. 61, represents a transverse section through a bud in which two pairs of metac- 

 nemes have appeared, in addition to the six pairs of protocnemes. Owing to the difference of 

 level at which the corresponding details occur on the inner and outer surface, as a result of the 

 obliquity of growth, it is usually impossible to obtain all that is desired in one section: the figure 

 i- therefore a combination of the inner and outer regions of sections at slightly different levels. 

 Above the bud is a portion of the edge-zone of an adjacent polyp. 



