1890-91.] Tlie Structure and Life-History of a sponge. 429 



{Poterion Neptuni), measuring from three to four feet across, 

 — there is a corresponding variety of habit, structure, and 

 appearance. Sponges are usually not very interesting objects 

 to an unscientific observer, with their pale-green or Isabel- 

 white hues ; yet some possess beautiful tints in the living 

 state, as in the genus Halisarca, where we find such colours 

 as blue, carmine, purple, and rosy red. Again, as regards 

 their mode of growth, some spread over the surface in lichen- 

 like patches ; others grow in large amorphous masses ; while 

 the characteristic forms of northern latitudes throw out branches 

 or large finger-like processes, as in the well-known " Mermaid's 

 glove " {Chalinula oculata) of the Shetlanders. But there 

 is withal a certain similarity in their outstanding features, 

 sufficient to enable even the non-scientific observer to say with 

 confidence, ''That is a sponge ! " What is now attempted is 

 to give an outline of the typical structure and life-history of 

 these lowly and familiar objects, referring to the accompanying 

 microscopic preparations in illustration of most of the state- 

 ments made. Such an outline may, it is hoped, at once give 

 a fair idea of the subject, and prove interesting to members of 

 the Society who have not yet paid much attention to this 

 branch of natural history. 



A glance may first be taken at the place which sponges 

 occupy in the wide realm of nature. From the apparent sim- 

 plicity of their structure, and the fact that they are always 

 found, in the living condition, attached or rooted to some 

 foreign object, it was for long a moot-point whether sponges 

 were to be regarded as plants or animals ; and they were fre- 

 quently hustled backwards and forwards across the border-line 

 which is generally believed to divide these two great groups. 

 Not only have different authorities held conflicting opinions 

 regarding them, but the same naturalists, at different periods, 

 have inclined now to one side, now to the other. Thus 

 Linnreus, in the earlier editions of his ' Systema ISTaturre,' 

 classed them amongst the cryptogamic alg?e, but in the twelfth 

 edition of that work, published in 1767, he ranked them with 

 the zoophytes. Though Aristotle, 2000 years ago, placed 

 them in the animal kingdom, it is plain he too regarded 

 sponges and some other bizarre forms as partaking also of the 

 nature of plants — for which nondescripts, indeed, the convenient 



