282 DB J. H. ASHWORTH AND DR JAMES RITCHIE ON THE 



Specific Characters of Dicoryne conybearei (Allman), emend. 

 Syn., Heterocordyle conybearei of Allman and later authors. 



Trophosome. — The hydrocaulus springs from a network of creeping hydrorhizal 

 tubes, reaches a height of 4-8 mm., and is either simple or furnished with a few 

 branches which arise acutely from the stem and are seldom subdivided. A well- 

 developed perisarc is present, slightly and irregularly wrinkled throughout its length. 

 It is covered with a dense coat of foreign particles and widens at the base of each 

 polyp into a shallow, cup-like expansion. Up to four to eight polyps are borne on a 

 single hydrocaulus, and these are furnished according to age with from six to sixteen 

 tentacles in a single whorl.* 



Gonosome. — Blastostyles arise on the stolon and on the hydrocaulus ; their basal 

 portion is covered with perisarc which terminates in a cup-like expansion similar to 

 that beneath the polyps. Around the blastostyle the sporosacs, in general eighteen 

 to twenty-four and exceptionally as many as thirty-four to forty, are grouped in 

 a spherical or elongate cluster. The sporosacs arise from a zone encircling the 

 middle region of the blastostyle, the tip and base of which project beyond the 

 mature cluster. In the adult state the sporosacs are free-swimming, are furnished 

 with one tentacle, and are covered with cilia. Female sporosacs bear a solitary oocyte. 

 The structure of the sporosacs is of the simplest nature, as they consist of a single 

 layer of ectoderm between which and the endodermal spadix lies the oocyte or the 

 mass of spermatozoa. 



The inclusion of this species within the genus Dicoryne necessitates a slight 

 alteration in the generic characters as given by Allman and accepted by subsequent 

 writers. The new definition is as follows : — 



Dicoryne, Allman, char, emend, (including Heterocordyle, Allman). 



Trophosome. — Hydrocaulus consisting of simple or more frequently, in mature 

 colonies, of branched stems arising at intervals from a creeping filiform stolon, which 

 forms a close network. Hydranths fusiform, merging gradually into the hydro- 

 caulus, with a single whorl * of filiform solid tentacles (with a single series of 

 endoderm cells) surrounding the base of a conical hypostome. 



Gonosome. — Simple sporosacs, consisting of a single layer of ectoderm and an 

 endodermal spadix, between which the sexual products lie. The sporosacs are 

 borne in clusters on blastostyles which arise from the stolon or the hydrocaulus or 

 from both. At maturity the sporosacs, which are furnished with one or two tentacles 

 witli solid endoderm and are entirely covered with cilia, break away from their 

 stalks and are free-swimming. 



* In many hydranths there are longer and shorter tentacles alternating ; in life the longer ones? jn'obably pointed 



disUlly, while the shorter ones wen- directed more or less horizontally (see p. 200). 



