140 CLARKE ON HYDROIDS 



colony it was determined that terminal growth takes place by the development of a lateral 

 bud from a point on the terminal segment just below the annulated pedicel of the terminal 

 hydranth ; as this process elongates it is divided by four septa into four segments, from the 

 distal one of which a new hydranth is formed, so that each hydranth on the main stem has 

 in turn been the terminal zooid of the colony. From the series of figures 29 to 34 

 on Plate 9 some idea may be obtained of the rate of growth in the hydrocaulus of this 

 sjiecies ; figure 30 was taken eight hours subsequently to figure 28; figure 31 six hours later ; 

 figure 32 seven hours afterward ; figure 33 after a lapse of four hours and figure 34 seventeen 

 hours after figure 31 or forty-two hours later than figure 33. I also recorded the rate of 

 growth in the hydrorhiza which is indicated in Plate 9 figures 27 and 28 ; the 

 latter figure being made thirty-two hours after the other one. It should be remembered 

 that the colony upon which these observations were made was in somewhat abnormal con- 

 ditions. My specimens were procured from a depth of three to ten fathoms where the 

 temperature was considerably below that of the atmosphere. I was unable to have them 

 in an aquarium with a constant stream running through, and the water being changed but 

 a few times during the day the specimens must have been subjected to a much higher 

 temperature than they are generally accustomed to. It is possible moreover that a more, 

 rather than a less rapid growth may have thus been induced, as it is well known that many 

 hydroid colonies, especially of the Calyptoblastea, will, when stimulated by impure water 

 in aquaria, develop long, slender processes at a very rapid rate. They seem to be endeav- 

 oring to get into a region where better conditions for their welfare exist. 



Bougainvillea rugosa, nov sp. Plate 8, figs. 21 to 24. 



Trophosome. Hydrocaulus large and compound at the base, tapering to the distal end 

 where it becomes simple, rooted by creeping stolons and attaining a height of three inches ; 

 branches numerous, irregularly arranged, a few that arise from near the proximal end of 

 the main stem nearly equal the latter in length; most of the branches are short and deli- 

 cate, bearing small branchlets which give origin to three or four ultimate ramuli ; hydranths 

 fusiform with a rather small, conical hypostome, protected by an expansion of the perisarc 

 very much roughened by circular ridges, into which the hydranths are partially retractile ; 

 tentacles short and eight to ten in number. 



Gonosome. Planoblasts borne by the hydrocaulus on the ultimate ramuli below the 

 hydranths, having at the time of liberation a deep umbrella, somewhat pyriform ; hypostome 

 short and thick, chymiferous tubes four with circular canals, proboscidial tentacles four, cap- 

 itate, unbranched, marginal tentacles twelve, three of equal size at extremity of each 

 radial canal, where they originate from a common highly colored bulb ; ocelli developed at 

 the bases of those two tentacles of each group which become first and second as one 

 passes round the bell from left to right; with increased age they gain in size and the 



