7. Anthozoa (incl. Hydrocorallia). A. Zoantharia. 27 



torn off by muscular contractions. While the regeneration of small pieces in 

 M. agrees with that in S., tlte laceration pieces of A. are, after regeneration, 

 generally biradial, 4 complete mesenteries forming a group on each side of 

 the transverse plane, their longitudinal muscles turn away from this plane. 

 Each group resembles the single new zone of growth of the smaller pieces in 

 S. Consequently A. has 2 new zones of growth which nevertheless , as only 

 one stornodseurn is formed, usually regulate themselves to one animal. In one 

 case there was a third new growth zone, but the mesenteries were all arranged 

 round a single stomodseum. The socalled biradial type of formation of mesen- 

 teries (Hertwig, Boveri) did not arise ontogenetically, but is a regulation pheno- 

 menon connected with laceration. The author also deals with the longitudinal 

 division of Corynactis viridis and Paranemonia contarini and describes a double 

 embryo of Cribrina gemmacea. He discusses double formations and concludes 

 that such may arise in the Actiniaria in quite different ways, e. g. owing to 

 sudden interruption of longitudinal division. 



Torrey & Mery find that Sagartia davisi reproduces asexually by longitudinal 

 fission only. 3 types of fission are distinguishable. (1) Aboral-oral fission 

 by constriction, accompanied by rupture. This is preceded by arrangement 

 of the mesenteries about two centres. The fission plane passes through the 

 oral disc and nearly always through the mouth perpendicular to its major axis, 

 and when the polyps again divide the second fission plane is parallel to the 

 first. Such fission may take place before regeneration of a second siphonoglyph, 

 so that polyps may be produced which are aglyphic at first. Of 51 cases 

 examined in 10 the fission plane passed through exocoels, in 32 through ento- 

 coels and in 9 through an entocoel on one side and an exocoel on the other. 

 (2) Aboral-oral fission by constriction alone. This is not preceded by rearrange- 

 ment of the mesenteries. The prompt completion of the division (in 15 to 

 24 hours) usually leads to 2 polyps, but if before division is completed an 

 area of the pedal disc near the constriction becomes secondarily attached and 

 ceases to follow the motions of the portion of which it forms a part, a strain 

 is set up ending in complete rupture and formation of a third polyp usually 

 much smaller than the other 2. A fourth and a fifth may be so formed, but 

 the whole process is irregular. Regeneration succeeds fission of both these 

 types. The first pair of mesenteries arises in the middle of the regenerating 

 tissue formed along the line of fusion of the torn edges, then another mesentery 

 is formed on each side of this pair, and later other 2 appear. The first 

 tentacle arises between the first 2 mesenteries, then 2 others and 4 others 

 follow. (3) Fission proceeding from side to side, by rupture. This was observed 

 in an abnormal polyp which possessed a second mouth and set of tentacles 

 on the side of the column, produced as the result of a wound. The fission 

 plane passed between the 2 oral discs. From experiments it appears that an 

 interruption of the physical continuity of 2 portions of a polyp by means of 

 a cut parallel to the course which would be taken by a normal fission plane 

 tends to interfere with the physiological interaction of the two parts and to 

 initiate the process of fission. Heteromorphosis. 20 polyps were cut 

 transversely into oral and aboral portions. 9 of these oral portions were very 

 short, 4 rested with oral disc upwards, 5 with aboral end upwards, 2 of the 

 former but none of the latter developed hydranths in 5 weeks. Of 11 longer 

 oral portions, 4 rested with oral disc upwards, 7 with aboral end upwards, 

 in 4 weeks all the former had developed aboral hydranths , of the latter 5 

 developed aboral hydranths, 1 produced both foot and hydranth aborally and 

 1 was a normal polyp. Gravity therefore cannot determine the presence or 



