b AMERICAN ll\DKOIDS. 



Ions which arise from the stem tubes and arc directed downward "basalwarts." In many 

 cases th«se stolons arise at or inmiediately below the pedicel origins, reminding one of the con- 

 dition til at I have described as found in the polysiphonic stem of Serfularella gayi,' where the 

 peripheral tubes were seen to have their origin as stolon-like offshoots from just below the 

 bases of liydi-otheca3. An examination of a specimen of Ohelaria gelatinosa from Plymouth, 

 England, shows that the hydrorhiza or root of the colony is composed largely of these down- 

 ward growing stolons, as in the case of Sertularella gayi. Occasional cross connections of 

 , coenosarc are also seen and these were most evident in connections with the branching of the 

 stem or at the origin of the stolons. These however, were not truly cross connections, but 

 merely the extensions of the coenosarc of the stem into the branch or stolon. True coenosarcal 

 cross connections were also seen, however, by which one tube in the stem had direct commu- 

 nication with another. 



In some cases one of these stolons wiU bear a pedicel with its hydrotheca at one end while 

 the other end is growing downward on the surface of the compound stem, giving a curious 

 appearance of being "stuck on". 



In Obelia plicata the compound stem is composed of much stiffer, more rigid tubes, the 

 perisarc being thick and of a dark color, reminding one of the stem of Eudendrium. 



The hranches. — Although containing a number of the simplest forms the family Campan- 

 ularidse includes many of the most mtricately branching species fomid in the Hydroida. They 

 differ from many of the Sertularidse, however, in never showing the anastomoses of the branches 

 which at times form the curious reticulate patterns found in the genus Didyocladium and in the 

 remarkable form described by Jaderholm under the name of SertulareUa mirahilis. 



In many species the main stem is often imbranched and bears a pedicel on each mternode, 

 the pedicels usually bemg alternate m position. Among the more profusely branching forms 

 the genus Obelia shows the most striking examples. In 0. fiahellata, for instance, the branches 

 are divided and subdivided dichotomously until the final ramifications are reduced to the most 

 delicate tracery, each branch being like the palmate frond of a finely divided fern. 0. longissima 

 is even more slender and delicately branched, the branches having an approximation to a verti- 

 cillate arrangement. In our Obelia commissuralis the branches are arranged in an ascending 

 spiral and the branches themselves are geniculate, giving off ultimate branches of extreme 

 delicacy. 



The pedicels may be regarded as the ultimate branchings of the hydrocaulus. They vary 

 in length from 1 1 mm. in Oampanularia spiralis to practically nothing where the hydro thecse 

 are sessile, as in Obelia marginata. The chitinous perisarc of the pedicel is very greatly thickened 

 in some species, particularly in Orihopyxis (fig. 13) and Silicularia (fig. 8). The surface may be 

 perfectly smooth, as in Campanularia ritteri (fig. 10), or closely annulated throughout, as in 

 C. speciosa (fig. 9). The most common arrangement is to have one or two annulations just 

 below the hydrotheca and also at the base of the pedicel, leaving the median portion smooth; 

 and there is very commonly a globular amnilation just below the hydrotheca. In the branching 

 forms the pedicels are usually shorter than in the simple campanularians, and they never show 

 the remarkable thickening of the perisarc mentioned above. 



The hydrothecse. — There is much greater uniformity in the shape and size of these structures 

 in the Campanularidse than in either of the other families thus far considered in this work, and 

 they differ from these latter also in the fact that with a few exceptions, notably in the genus 

 Silicularia (fig. 8) they are radially symmetrical. Their typical form is campanulate, which 

 gives the name to the family, and the variations in form are usually in lengthening or shortening 

 the bell. In most cases they are longer than wide with the greatest diameter at the margin, 

 although in exceptional cases, e. g., Campanularia speciosa Clark (fig. 9) the greatest width may 

 be near the proximal end. The lengthening of the bell may result in a more or less tubular 

 structure, as in Campanularia ritteri Nutting (fig. 10), where the sides are approximately par- 

 allel; or in an urceolate form, as in C. speciosa. Sometimes the outline m lateral view is sub- 

 triangular, as in Obelia flab ellata (fig. 15), m which the hydrothecse are often as wide as long. 



1 See Part II, p. 6. 



