192 Proceedings of the 



III. On Hydractinia Echinata. By T. Strethill Wright, M.D., 



Fellow of the Royal College of Physicians, Edinburgh. 



Explanation of Plates. 



Plate VIII. 

 Fig. 1. Diagram showing the various polypoid forms observed on the (female) 

 polypary — a, spiral polyp — b, reproductive polyp — c, alimentary 

 polyp — d, sessile ovary — e, tentacular polyp. 



2. Solid grooved papilla of corallum. 



3. Hollow papilla of corallum. 



4. Ideal section of the extremity of one of the propagative stolons — a, 



" colletoderm" — b, corallum — c, ectoderm — d, endoderm. 



5. Spermatic capsule of reproductive polyp of male polypary — a, ecto- 



derm — b, muscular coat — c, endoderm — d, gelatinous plasma, in 

 which spermatozoa are developed. 



6. Ovarian capsule of reproductive polyp of female polypary — a, ectoderm 



— b, muscular coat — c, endoderm — d, ova. 



7. Fecundated ovum segmented by yelk cleavage. 



8. Larva studded with motionless " palpocils." 



9. Young polypary and polyp. 



10. Spiral polyps covered with large thread-cells. 



11. Large and small thread-cells. 



Plate IX. 



Fig. 12. Young polypary attached to side of tank, showing tubular net-work of 

 the endoderm. 

 13. Diagram showing the situation of spiral polyps a, and tentacular 

 polyps b. 



1. In rock pools left exposed by the retiring tide on the 

 shores of the Firth of Forth, numerous Paguri, or hermit crabs 

 are found, inhabiting old turbinate shells, formerly occupied 

 by various species of Buccinum and Fusus. The rough and 

 worn surfaces of these shells also form convenient homes for 

 a great variety of animals, and frequently afford a strange 

 scene of thronged and busy life. In the spring they present 

 the naturalist with a rich field for observation. He will find 

 the fixed and blind Balani, hidden in their mailed armour, 

 winnowing the water with their fan-like cirri, and vomiting forth 

 swarms of bright-eyed and actively swimming larvae. There 

 the Spio incessantly tosses about her long arms ; the Serpula 



