Homes or Tubes formed by Annelids. 5 



Tlic ti'iitli LC'"ii|' hk-IiiiIl'S those wliiili perforate rocks .iiid 

 live In tlio tiimiels thus tashioMcil, uikI which \vc exu'.niiicil 

 more |)articiM;irly in the Introductory lectun; at the euni- 

 niencenient of last session. A typical torm is Dodecaceria, 

 while Sabella sa.ricuva anil Poh/dora not only bore in rocks 

 but append tubes to their tunnels. 



The last, or eleventh, series is one of the most interesting, 

 since its members — ilcelining to form homes for themselves — 

 become messmatt's (or, as they were called by Van lieneden 

 of Louvain, commensalistic forms) of other animals — like the 

 Nereid {Xerei/epas fucata), which shares the shell of the 

 whelk with the hermit-crab, or those annelids (chiefly 

 belonginf^ to the Polynoidte) which are only found in the 

 tulx'sof others. In this grou[) are Poh/noi; Johnstoni^ P . sco- 

 htpendrina, Antinu'e parasitica (under the scales of Lepida- 

 mttria), llermadion pcUucidumj Pohfno'd eaplectelhn^ Anoplo- 

 ncreis (Giard) on Balano<jlossus, and similar forms. 



With the bri(!f space at our disposal, however, it is mani- 

 festly impossible to do anything like justice to so many 

 diverse heads, and accordingly I have thought it best to 

 select a few of the most interesting types amongst those 

 whose homes — formed of the body-secretion — present great 

 regularity, or in which the foreign elements, mixed with the 

 secretion, assume wonderful design or complexity. These 

 mostly range themselves under the sixth and seventh heads 

 already mentioned. 



In surveying the memliers of the Invertebrate series of 

 animals wliich are remarkable for their skilfully constructed 

 homes, it is found that the majority have well-formed eyes, 

 such as the amphipods, ants, bees, wasps, caddis-worms, and 

 spiders. If, on the other hand, we glance at the marine 

 annelids, it is curious that those with the largest and most 

 complex eyes are entirely pelagic {e. 7., the Alcioi)ida3) and 

 form no protective abode whatever. Though furnished with 

 bright ]>igment their translucent bodies are even less con- 

 spicuous than the huge globular eyes, the pairs of which may 

 be arranged so as to look laterally and ventrally. Those 

 annelids, again, which construct complex tubes have eyes of 

 a very elementary jnvttern — masses of pigment — with a 

 simple capsule, and some of the most skilful are entirely 

 devoid of them. The tactile sense, however, seems to be 

 highly developed, so that, to a considerable extent, it takes 

 the place of the other senses. 



The annelids of the first group at present selected for 

 consideration construct their tubes of large shell-fragments. 



