HYDROIDA II 



79 



apophyses and hydrocladia; here again we fmd the supracalycine sarcothecse particularl) well devel- 

 oped, in the same manner as over the apophyse, and more than on the normal cladial internodia; at 

 the same time there is not the slightest indication of any such pattern as that which Nutting has 

 taken for a sarcotheca. The abortive hydrotheca probably forms a parallel to the apophysal "mamelon" 

 in Nemertesia and Polynemertesia, and would seem to throw some light on its origin. 



There is considerable variation in the appearance of the hydrotheca.* (fig. XL) especially owing 

 to the fact that the abcauline keel and its prolongation vary very greatly both in length and breadth ; 

 the outgrowth may be broad and blunt, or more slender, and running out to a point. It forms an 

 incurvation in the wall of the hydrotheca; at its base, the hydrotheca is furnished with a sharply cut 

 tooth, directed obliquely inward and forward, and between this and the internodium the edge shows 



Fig. XL. Aglaopliowpsii cornuta, a Basal part of a hydrocladium with the phylactogonium and a 

 gonotheca in side view from "Ingolf" St. 98 (X 40). -- b Front view of a hydrotheca from the 

 same colonv (X 60). — c Side view of a hydrotheca from the same colony (X 60). — d Hydro- 

 theca from a colonv from "lnoolf" St. 25, side view I'X 601. 



as a rule four teeth on either side, which become broader and lower nearer the hydrocladium. The 

 innermost tooth on either side, and at times the one next to it, can even now and again be entirely 

 effaced, so that only two abcauline teeth can be distinguished on either side. - The proximal sarco- 

 theca also varies considerably, diverging now more, now less widely from the hydrotheca, and having 

 a free portion of varying length. 



The basal internodium of the hydrocladium has a different structure owing to the position of its 

 proximal sarcotheca. This is shifted to the obliquely upward trending hydrocladium, — the side away from 

 the stem — and is also somewhat smaller than on the following internodia. The cause of this must 

 be sought in the growth of the phylactogonium. 



The phylactogonium (fig. XL a) is segmented and has only hydrothecse on two of its branches; 

 on one of them at times two, but as a rule only one on each; they are surrounded by the usual three 







