260 W. D. Lang — On Stomatopora antiqua. 



Applying this principle, we may say that at every branch in 

 a colonial form such as we are considering there is a potential 

 recapitulation. Now the slight tendency to pyriformation at 

 dichotomies 1 and 2 in the present form shows that the general 

 cylindrical stage was preceded by one which was more or less 

 pyriform. The tendency, then, at each dichotomy is to recapitulate 

 this stage. The potential recapitulation occasionally becomes actual, 

 and appears as the sporadic production of somewhat pyriform zocecia, 



A third explanation of these sporadic zooecia is that they are 

 simply gonoecia. And the fact that in all organisms reproductive 

 tissue arises from undifferentiated cells may furnish a hint as to 

 why primitive characters are shown in reproductive zooecia. 



Having indicated the directions in which difficulties may be 

 expected in applying the scheme of measurement advanced in the 

 former paper, it is possible to limit Haime's species by the following 

 definition, which takes into account stages of growth : — 



I. Stomatopoea antiqua, Haime. (PI. XIV, Figs. 2, 4, 5, and 7.) 

 Characters. — Zoarium loose and spreading, the first dichotomy 

 being after Type I at an angle of about 180°. The Intermediate 

 type of branching appears at the third or fourth dichotomy, and 

 Type II by the fifth or sixth. As has already been remarked, the 

 branching is often somewhat irregular, so that the exact type is hard 

 to determine. There are two peristomes before the first dichotomy,, 

 and generally one between the first and second. The acme is 

 reached with three or four peristomes between the third and sixth 

 dichotomies ; after which, with a small check at about dichotomy 

 7, the number of peristomes between each dichotomy rapidly 

 diminishes. The proportion of the length of the zooecium to the 

 breadth is very variable, but by examination of a number of 

 specimens a general sequence can be recognised. That of the 

 protoecium is about 1, of the second zocecium about 2. The acme 

 of length is at dichotomies 1 and 2, where it is from 2 to 2J. 

 From dichotomy 2 it gradually diminishes until it is only 1^ at 

 dichotomy 9. The shape of the zocecia is irregularly cylindrical, 

 with a slight tendency to pyriformation between dichotomies 1 and 2, 

 and with an occasional irregular pyriform zooecium as already 

 noticed. The ornamentation is a very slight, fairly fine ribbing, but 

 the zooecia often appear smooth, owing to bad preservation, for 

 which reason it is bard to see any regular change in this character 

 during the growth of the colony. The sides of the zoarium tend to 

 be flattened on to the object which it encrusts. 



For comparison the original description by Haime is here 

 given' : — 



" Les raailles de ce testier ont une tendance k se rapprocher de la 

 forme d'une rhombe irregularier, et dont les angles seraient emousses. 

 Les sept premieres testules produisent deux bourgeons ; il arrive 

 frequenment que deux testules jumelles soient un peu inegales en 

 grosseur, et restent presque completement accolees I'une a I'autre ;. 

 1 J. Haime: loc. cit., pp. 162-163. 



