988 MR. R. KIRKPATRICK AND DR. J. METZELAAR 



consideration, judging each case on its own merits. A good 

 example of the specific value of zoarial characters is aiTorded by 

 Lepralia hifurcata Waters, found in deep water oft" Capri. Here 

 we have a typical Lepralia^ but one that alwaj'S grows in a very 

 definite, peculiar, and characteristic Avay, viz. as a bifurcating 

 colony with two little wings. No matter how closely the 

 characters of the individual zooscia resemble those of some par- 

 ticular encrusting Lejircdia, it would be difficult to regard the 

 bifurcating colony as a mere variety or variation of the en- 

 crusting one. Similarly, we regard the dense, stony, multi- 

 laminate Polyzoon from Cape Blanco as specifically distinct from 

 the slender, thinly encrusting C. lacroixii, the modified character — 

 if we may adopt the neo-Lamarckian line of thought — having 

 perhaps restdted from epcecal, e. g. well-fed life. 



Biology. — Again, the adoption of the name " comrtiensale " 

 might be considered a doubtful proceeding. We think the name, 

 however, to be convenient, not only from the point of view of 

 easy identification, but justifiable as indicating the real relation- 

 ship existing between the Polyzoon and the Crustacean. There 

 is evidently no question of true symbiosis or mutualism sensu 

 strictiore, if we define that as " legal relation betweeia two 

 difierent organisms," principally, because Petrochirus granidi- 

 mamis can live and thrive without C commensale. Leaving the ■ 

 young Crustacea aside, we find the adults associated with the 

 sponge Suherites domtmcula, the compound zoantharian Corticifera 

 lutea, and the Polyzoon Lejyralia edax. 



But the reverse does not seem to be the case. Polyzoa growing 

 on the hydroids and corals of the Vermeulen-expedition did not 

 include C. commensale among them. Nor did we notice it upon 

 living molluscs from the same localities. Possibly the Polyzoon 

 could survive for a time on an untenanted shell with much 

 diminished vitality, but so far there is no evidence on this point, 

 although we must take into consideration that the West African 

 material has been collected by one who was not a zoologist. 



According to Prof. Calvet, any smooth surface is suitable to the 

 Membraniporee, and " associations of hermit-crabs and Polyzoa 

 are common enough." Even so, we never saw them before in 

 such a definite non-accidental mode and shape. The Pagui^o- 

 Polyzoan association described here appears to be a definite and 

 not an accidental one, the Ci'ustacean and Polyzoon being more to 

 each other than casual messmates ; for it is certain they derive 

 special advantages from each other's presence. 



Hermit Crabs are widely distributed all over the world, and 

 are notorious for their militant and aggressive nature. Ensconced 

 in their shells they are veritable tankers, spreading dismay 

 among their helpless victims. Every now and again, when the 

 soldier has to leave his fortress, his softened body is exposed to 

 danger. But frequently some other organism (Sponge, Coelente- 

 rate or, more rarely, Polyzoon) adapts itself to the shell, and 

 gradually acqiiires certain special characters. The enci'usting 



