ACQUIRED SPECIFIC REACTIONS TO COLOR 151 



became apparent to the writer, after a preliminary study of 

 the habit of decoration in Oregonia gracilis, that a distinction 

 should be made between what may be called active and passive 

 decoration. Cursory observation of the crabs is sufficient to 

 reveal the curious habit or instinct of self adornment. The 

 animals do actually "plant out" algae, etc., upon their bodies. 

 On the other hand, the writer doubts whether barnacles, tuni- 

 cates, sponges, hydrozoa and tubeworms are placed upon the 

 carapace by the active effort of the animal. Certainly, the 

 writer never observed an active decoration of the crabs with 

 such material, during a period of observation extending over 

 seven weeks. Triton eggs were the only objects of a similar 

 nature which were so used. On the other hand, the attachment 

 of forms which simply happened to settle down upon the crab 

 as it rested upon the bottom of the aquarium, was repeatedly 

 observed. In one instance a sea-anemone (Metridium) 35 mm. 

 in length when expanded, attached itself to the shell of a 

 Mytilus which was already attached to the carapace of an 

 Oregonia gracilis when captured. Passive decoration 4 must 

 therefore be recognized. 



The manner in which the active decoration or "planting 

 out" takes place is worthy of description. Minkiewicz 5 sup- 

 plementing his own observations by those of Aurivillius, has 

 described the movements very exactly. " Le procede de de- 

 guisement a ete tres exactement decrit par Carl Aurivillius 

 chez Hyas araneus L. de la famille des Majinae. Comme il 

 est presque identique a celui de Maja, je n'y insisterai pas 

 beaucoup. Ayant trouve une algue (n'importe laquelle: rouge, 

 brune, ou verte — cela depend seulement de 1 entourage), le 

 crabe l'attrape avec ses pinces greles et allongees, la met d'abord 

 dans ' sa bouche ' et en la tenant par un bout avec ses maxilli- 

 pedes se met a la dechirer en morceaux avec les deux pinces, 

 l'une l'attirant vers sa carapace, l'autre la repoussant. 



4 Since this paragraph was written, the author has found that C. Aurivillius 

 made the same distinction and employed the same words as are here used, "Unter 

 solchen Umstanden stellt sich die erste und zwar die wichtigste Frage folgender- 

 massen auf: Verhalt sich die Krabbe aktiv oder passiv hinsichtlich des Kleides 

 fremder Organismen, welches ihren Korper bedeckt " P. 6, Die Maskirung der 

 Oxyrhynchen Dekapoden durch besondere Anpassungen ihres Korperbaues ver- 

 mittelt. Svenska Vet. Akad. Handl., vol. XXIII. Stockholm. 



5 Analyse Experimental de l'instinct de Deguisement chez les Brachyures 

 Oxyrhynques. (Note preliminaire.) Arch, de Zoologie Exper. et Gen., t. 7, p. 36. 



