the mermaid's glove, the elephant's ear (p. 64), 

 and Venus' flower basket (p. 61). Sponge colora- 

 tion is extremely variable, even in the same species. 

 Deep-water forms are likely to be drab grays or 

 browns, sometimes white; but in shallow waters many 

 of the encrusting sponges tend to take on brilliant 

 hues: sulphur yellow, bright pink, scarlet, deep reds, 

 all shades of purple, and beautiful greens. Both ma- 

 rine and fresh-water sponges often harbor algal cells, 

 and a fresh-water species that appears green in full 

 sunlight is colorless on the underside of the same 

 rock. The horny sponges of commerce shade from 

 light browns to jet black. 



All sponges are capable of sexual reproduction, 

 and though most produce eggs and sperms in the 

 same body, they do so at different times, so that 

 cross-fertilization occurs. The small motile sperms 

 enter other sponges with the ingoing current, and the 

 food-laden fertilized egg develops into a tiny flagel- 

 lated larva that leaves with the outgoing jet. After 

 swimming about for some time the larva attaches 

 and grows into a young sponge. This serves to dis- 

 tribute the wholly sedentary sponges to new habitats 

 and gives the young an opportunity to move over a 

 bit before setting up shop in competition with their 

 parents and relatives. 



Animals as loosely put together as the sponges can 

 be expected to have exceptional capacity for asexual 

 reproduction and for the regeneration of injured or 

 lost parts. Any part of a sponge can grow into a 

 whole animal, though the process is slow and the at- 

 tempts to raise commercial sponges from small pieces 

 have met with only limited success (p. 66). When 

 sponges with very high regenerative powers are 

 squeezed through silk bolting cloth, the separated 

 cells come together in small clumps, then in some- 

 what larger masses, and finally grow into complete 

 sponges. All fresh-water sponges, and some marine 

 ones too, regularly produce asexual reproductive 

 bodies, called gemmules (p. 64). When conditions 

 of life become unfavorable many sponges constrict 

 off the tips of their branches or simply disintegrate 

 and leave behind little masses of cells. These round 

 up. remain dormant for a while, and with the return 

 of better times regenerate into new sponges. Small 

 sponges may not outlast a single year, but it is hard 

 to believe that some of the largest sponges can attain 

 their magnificent size without continuous growth over 

 twenty-five or even fifty years or longer. 



Most zoologists are repelled by the prospect of try- 

 ing to identify sponges that fit their shape to the sub- 

 strate on which they grow, vary in size according to 

 the local prosperity of a spot they attached to when 

 still a larva, and vary in color for reasons that are not 

 always clear. Rare sponges dredged from deep wa- 

 ters are often easier to identify superficially than are 

 the compact encrusting types found between tide 



marks. Sponge specialists have resolved the problem 

 by basing the identification of species mainly on the 

 chemical composition and geometrical configuration 

 of the skeletal parts, which are consistent, highly dis- 

 tinctive, and readily preserved. It is relatively easy 

 to set aside two of the classes: the simpler and mostly 

 smaller forms, the calcareous sponges, and those sili- 

 ceous sponges that we call glass sponges. All those 

 siliceous and horny sponges left over are put into a 

 third and much the largest class, which is less homo- 

 geneous and which has been divided up in somewhat 

 different ways by the various specialists. The names 

 of even the largest groupings are not yet stabilized. 



The Calcareous Sponges 



(Class Calcarea) 



The calcareous sponges, as biologists call them — 

 or the chalky or limy sponges, as they are popularly 

 named on English-speaking shores — have spicules 

 that are largely of crystalline calcium carbonate. 

 They are all small marine sponges, ranging in length 

 from about Vs of an inch to 5 inches at most. Usu- 

 ally white or of drab color, these inconspicuous little 

 vases or tubes, often of bristly texture, grow singly, 

 in clusters, or as branches of a bushy or compacted 

 colony. Some of the genera are widely distributed 

 about the world in shallow waters, except where the 

 salt content is too markedly lowered by admixture 

 of fresh water. 



Whether or not a sponge has spicules of calcareous 

 content can easily be determined by teasing apart a 

 bit of sponge on a microscope slide, adding a drop of 

 acid, and watching through the eyepiece to see if 

 the spicules dissolve with the effervescence of carbon 

 dioxide released from calcium carbonate. 



Around the opening or vent at the top the cylin- 

 drical body is constricted a little, and often bears an 

 erect fringe of especially long needle-like spicules. 

 On the body, however, the most common type of 

 spicule is three-rayed, with the rays at equal angles, 

 T-shaped, or Y-shaped. Three-rayed and less nu- 

 merous four-rayed spicules are distributed through- 

 out in such a way as to strengthen and support the 

 fragile structure of nonliving gelatinous matrix and 

 delicate living cells. The surface may be strength- 

 ened by a special layer of spicules or by a parallel 

 arrangement of the rays of many body spicules. Of- 

 ten long, hairlike spicules protrude through the body 

 surface, giving it a hairy or bristly texture. 



The simplest of shore sponges belong mostly to the 

 genus Leiico.solenia, a name that means "white 

 pipes." But these sponges are so small and incon- 

 spicuous that they have never attracted much atten- 

 tion from fishermen and others who bestow common 



[59 



