78 MARGARET C. COLLCUTT. 



of the skeleton, and here connected the polyps with one 

 another. 



The earliest reference we have toHydractiniais that com- 

 prised in a few lines by Fleming (1) in 1828; this observer, 

 however, regarded the horny crust of Hydr actinia as being 

 a polyzoon ectocyst, and assigned to it the name Alcyonium 

 echinatum. 



This view of the nature of the hydroid was also held by 

 Johnson (2) in 1838. 



Van Beneden (4), in 1841, first gave the generic name of 

 Hydractinia to the hydroid, and wrote a paper on the 

 structure of the egg. He regarded the sporosacs borne round 

 the sides of the reproductive polyp as " eggs," but gave no 

 description of the structure of the colony. 



Hassall (5), in 1841, described, under the name '' Echino- 

 chorium clavigerum," a hydroid found in Dublin Bay 

 adherent to empty univalve shells, and which is, according to 

 Allman (13), the "Hydractinia, sp." of Van Beneden. 

 According to Hassall the colony consists of a " polypidom 

 muricated with rough, spinous papillae about a line in height. 

 There are numerous indentations on the surface of the polypi- 

 dom, in each of which the base of a polyp is inserted ; this 

 latter is about a quarter of an inch in height, and is of a white 

 colour; its head is somewhat enlarged, and is surrounded with 

 numerous contractile club-shaped tentacula ; the number of 

 these varies considerably, but frequently amounts to between 

 twenty and thirty. The tentacles are not arranged in any 

 determinate order, but are variously disposed. Whether the 

 polyps are separate or united at their bases I am unable to 

 say." His accompanying figure represents nutritive polyps 

 and ridged spines on a reticulated base. 



Philippi (6), in 1842, described as " Dy smorphosa con- 

 chicola" a hydroid from the Bay of Naples; his description 

 is short, but he recognised the fact that the polyps are con- 

 nected at their bases. 



De Quatrefages (7), in 1843, described Hydractinia under 

 the name of Synhydra parasites in the most comprehensive 



