336 REPORT— 1864. 



outer membrane or any other part of the EcJiinus. At the same time it is clear 

 that there is some connexion between the pecuhar habitat selected by the 

 Stilifer and its food ; for if it subsisted on any living organisms, it would 

 hardly confine itself to Echinoderms, but have a more varied range of 

 habitat. Such shelter as an Echinus or Asterias could afford might be as 

 easily obtained in crevices of rocks or in the cavities of deserted shells. Con- 

 sequently, although I do not consider this a case of true parasitism, like 

 that of the mistletoe among plants, neither would I refer it to epiphytism, 

 like that of a tropical orchid. It rather reminds one of the scavenger-habits 

 of dung-beetles. 



I have in another place* endeavoured to show that the pretty little bivalve 

 shell called Montacuta suhstriata, which also infests various Echinoids, is not 

 really a parasite. This always occupies a different part of the Echinus from 

 that where the Stilifer take up its abode ; it adheres by its byssus to the 

 ventral spines near the opening of the mouth on the under side. Here it 

 probably avails itself of the current or indraught excited by the ciliary action 

 of the Spatanr/tis or other Echinoid for its own purposes ; and both partake 

 of the same food in amicable but unconscious relation to each other. As 

 far as I have been able to observe, the Stilifer does not cause more inconve- 

 nience than the Montacuta to its not unwilling host. 



The suctorial proboscis, as well as the want of a denticulated tongue in 

 Stilifer Turtoni, strengthens the supposition that its food consists of extremely 

 soft or semifluid matter, and not of organisms which have any degree of 

 solidity. Dentalium, which preys on Foraminifera and other minute animals, 

 has (according to Lacazc-Duthiers) a very complicated lingual apparatus ; 

 and even the little liissoa, which feeds on seaweeds, often of the most 

 delicate and filmy texture, possesses a pair of horny jaws and a tongue armed 

 with a strong central tooth, which is flanked on each side by a formidable 

 row of serrated lateral teeth. Stilifer has no jaw or tooth of any kind. 



The late Mr. Stewart, of the College of Surgeons (whose untimely death 

 is still deplored by all who study the Eritish Echinodermata), was of opinion 

 that Stilifer Turtoni infested Echini for the sole purpose of depositing its 

 spawn. We know, from the observations of Mr. Peach, fhai Lamellctria per- 

 spicua frequents the shore at Wick, between tide-marks, every siimmer, and 

 makes a nidus for its spawn in a species of Botryllus. But Lcnnellaria is 

 not, like Stilifer, restricted to a particular habitat. The former attaches 

 itself to the iindcrside of loose stones, and is also found generally distributed 

 over the sea-bed, except perhaps in the spawning-season. The Echini on 

 which Stilifer Txhrtoni have been taken are very rarely covered with spawn : 

 and Stilifers of all ages, from one to half-a-dozen, occur on Echini, but 

 nowhere else. 



The fecundity of Stilifer is very great ; and it therefore ought not to be a 

 rare shell. I counted at least one hundred fry in one of the clusters of spawn 

 on the back of the Shetland sea-egg ; and as there were 41 of these clusters, 

 this would yield a prospective harvest of more than 4000 specimens — enough 

 to supply almost all the conchologists in the world. Moreover one of the 

 adult Stilifers appeared to be full of spaAvn. As the Echimis probably could 

 not accommodate more than half-a-dozen Stilifers when they came to matu- 

 rity, what would have become of the rest, supposing any of them escaped 

 being the prey of other animals ? Would they migrate, and form colonies 

 on other Echini ? They have feet and eyes ; and suitable habitations are not 



* British Conchology, vol. ii. p. 208. 



