THE BRITISH SPONGES. 11 



grow upon irrecognizable. Even of the more figured spe- 

 cies, when the branches of the same individuals, or of two 

 individuals of the same kind, come into accidental contact, 

 they speedily coalesce, and the union is so natural and 

 perfect that no difference of structure — not even an ideal 

 line — indicates the original place of meeting, while the 

 altered form may occasionally perplex the nomenclator : 



" Nam mista duorum 

 Corpora junguntur, faciesque inducitur illis 

 Una. Velut si quis conducta cortice ramos 

 Crescendo jungi, pariterque adoleseere cernat. 

 Sic ubi complexu coierunt membra tenaci, 

 Nee duo sunt, et forma duplex, nee fsemina dici. 

 Nee ptier ut possint ; neutrumque, et utrumque videntur."* 



But this intimate union is only between individuals of the 

 same species, for " different species of sponge do not imite 

 together when they come into contact : they form a slight 

 adhesion, but the line of separation is easily traced, and 

 they can be disunited without laceration, AVhen the 

 Spongia tomentosa meets the Spongia papillaris, the mar- 

 gins of both adhere together, rise a little from the rock, 

 and proceed directly outward, as if endeavouring to sur- 

 mount each other, till their contest is arrested by the ac- 

 tion of the waves, which would soon tear off the unsup- 

 ported margins, if they proceeded outward to any consider- 

 able extent." f I have seen these facts strikingly illustrat- 

 ed with Halichondria tomentosa and H. sanguinea, which 

 grew intermingled in such a manner that they had formed 

 a specimen resembling the map of a county where every 

 riding was coloured or white or red, and where the boun- 



* Ond. Metam. lib. iv. ix. 1. .373-9. 

 t Edin. Phil. Journ. xiv. p. 115. 



