326 Mr. Jeffreys on Stilifer, 



truded for the purpose of seeking this nourishment. I neea 

 not say that the reputation of Dr. Fischer as a physiologist, 

 especially with regard to the Mollusca, makes any opinion of 

 his on such subjects very valuable. I share his incredulity as 

 to Stilifer being a parasite in the ordinary meaning of the 

 word ; but my impression is that it feeds on the excretions of 

 Echinoderms, and not on animalcules or other organized and 

 living matter with which sea-water abounds. It has never been 

 found except on Echinoderms, or imbedded in their rays or 

 spines. All the specimens of Stilifer Turtoni which I have seen 

 in situ (and they have been rather numerous) occupied the upper 

 sides of Echini, in the area of the vent or anal opening. The 

 Echini so infested appeared to be invariably in perfect health 

 and vigour. The Shetland specimen of E. Dr'ubachiensis was 

 carefully watched by me for more than twelve hours. Its tubular 

 suckers and pedicellariaj continued in active although intermit- 

 tent motion during all that period. The Stilifers were nestling 

 or slowly crawling about among the spines ; but they did not 

 touch any of the suckers of the Echinus, which, being retractile, 

 could easily have been withdrawn into the test; nor could I 

 detect either of the mollusks in the act of feeding on the outer 

 membrane or any other part of the Echinus. At the same time 

 it is clear that there is some connexion between the peculiar 

 habitat selected by the Stilifer and its food ; for if it subsisted on 

 any living organisms, it would hardly confine itself to Echino- 

 derms, 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 para- 

 sitism, 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 elsewhere * endeavoured to show that the pretty little 

 bivalve shell called Montacuta substriata, which also infests 

 various Echinoids, is not really a parasite. This always occupies 

 a different part of the Echinus from that where the Stilifer takes 

 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 Spatangus or other Echinoid for its own purposes ; 

 and both partake of the same food in amicable but unconscious 

 relationship to each other. As far as I have been able to observe, 

 the Stilifer does not cause more inconvenience than the Monta- 

 cuta to its not unwilling host. 



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

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



