138 CLARKE ON IIYDROIDS 



Sytlactis arge, nov. Bp. Plate 8, figs. 18 to 20. 



Trophosome. Hydrocaulus undeveloped; hydranths with very much elongated, slender 

 bodies, occurring in colonies of ten to thirty tentacles, arranged in two verticils below the 

 hypostome, from six to eight in each circlet, those of the lower circlet sometimes shorter 

 than those of the upper one ; lrypostome large and rounded at the distal extremity. 



Gonosome. Sporosacs developed on the bodies of the hydranths beneath the tentacles ; 

 two are first developed from opposite points on the hydranth and then two others, also 

 opposite one another and on different sides of the hydranth from the first pair, make their 

 appearance ; the gonophores are quite well developed, having a large cavity, and four radial 

 canals connected distally by a peripheral canal; slight processes project from the rim of the 

 bell, which appear to be rudimentary tentacles ; a large number of planulae developed in 

 each female gonophore and these may be liberated while it is attached or after it becomes 

 free ; if the planulae are liberated whde the gonophore is attached, the latter never becomes 

 free, but in many cases the gonophore becomes freed from the hydranth and with its freight 

 of planulae leads a free-swimming life. 



Color. The entire colony a delicate opaque white. 



Development of gonosome. June and July. 



Habitat. On stems of Zostera marinum. 



Locality. Crisfield, Maryland, on the Chesapeake Bay. 



I became very much interested in this hydroid after seeing under the microscope a 

 gonophore detach itself from the hydranth on which it had developed and swim away 

 free. It accomplished this by a considerable number of very energetic, convulsive con- 

 tractions, which were sufficiently violent to rupture its peduncle. I had often seen the 

 planulae discharged from the attached gonophores and was much surprised to see in a 

 number of cases, and where the specific identity of the different colonies was undoubted, 

 that the gonophores with their contained planulae became detached. 



Another remarkable habit possessed by this species consists in the detachment of the 

 distal portion of a hydranth, which settles down in some new locality and gives rise to a 

 new colony. This takes place in this way : a constriction appears around the body of a 

 hydranth; from a point just above which two or three cylindrical processes are 

 developed which are to serve as a hydrorhiza to the new colony ; the constriction then 

 becomes complete and this short-bodied hydranth is carried by the currents to a consider- 

 able distance, perhaps, before it attaches itself by means of its hydrorhiza, when by growth 

 and budding it soon forms new colonies. 



This method of multiplying colonies and of planting them in new and possibly distant 

 places is a new feature in the hydroids. In Schizocladium there is an approach to this 

 same thing, but even in that case the method is distinctly different. 



In the possession of gonophores which may or may not become free, we are reminded 

 of the Syncoryne mirabilis of L. Agassiz, and the facts in this case lend support to the 

 characters claimed for S. mirabilis. I greatly regret that my investigations upon this 

 interesting form were so suddenly terminated. I was obliged to leave the locality where 

 this species is found at a few hours notice, and have never found an opportunity to continue 



