HABITS OF THE FOUR-HORNED SPIDER-CRAB. 251 



hairs on and in the region of the rostrum form two especially 

 long and strong rows, and it is here that the largest and heaviest 

 masses of seaweed are placed by the Spider-Crab. Indeed, the 

 disguising material fastened on this region is usually of such a 

 length that it stands out, often for as much as four inches, in 

 front of the head in a peculiar and characteristic manner. The 

 Halichondria, Spirorbis, and Botryllus mentioned above were 

 actually attached to, and growing upon, the Spider- Crabs, but 

 in all the other examples which I have been able to examine, the 

 ends of the disguising materials were merely thrust in the alleys; 

 and it is doubtful whether the Spider-Crabs had placed upon 

 themselves any of these three animals, the two last not being 

 attached by hooks at all, but lying flat on the hinder part of the 

 carapace. Bell declares that there is no doubt that plants actu- 

 ally grow upon Pisa tetraodon, and are attached by roots,* and 

 other writers have adopted this statement. In specimens pre- 

 served dry the disguising materials are often stuck upon the 

 body of the Spider-Crab in such a way as to give the impression 

 on slight examination that in life they actually grew on the 

 crustacean. The point deserves investigation by one who can 

 study numerous fresh specimens. Aurivillius, who gives a de- 

 scription of the distribution of the hooks in P. tetraodon, and a 

 figure of their arrangement in P. armata, says t of the former 

 species : " Die untersuchten Exemplare sind mit Hydroiden oder 

 Algen reichlich maskirt ; es sind dabei die Doppelreihen der 

 Bostralhakchen zur Befestigung wahrer Federbiische von 

 Hydroiden verwendet, deren Spitzen allesammt nach vorne frei 

 hervorstehen, die abgebrochenen Enden nach hinten in die 

 Furche zwischen den Hakchenreihen gelegt." I 



There appears to me to be little doubt that the arrangement 

 of the hooks in alleys not only affords the Spider-Crab a ready 

 means of affixing disguising materials upon its body, but also 

 of enabling it to escape by sudden detachment of the materials 

 if they should be seized by an enemy. Their use in the latter 



-;; Ibid. p. 25. f Op. cit. p. 49. 



I "The specimens examined are richly masked with hydroids and 

 algse ; the hydroids are fastened to the double series of rostral hooks in the 

 manner of feather-brushes whose points all stand out freely in front, wbile 

 their broken ends lie in the furrow between the series of hooks behind." 



