NATURE STUDY. 



Volume I. NOVEMBER, 1899. Nun her 10. 



SYSTEMATIC ZOOLOGY FOR TEACHERS. 



BY 



C. J. Matnabd. 



Forms and Species of Stongi-s. 

 ( continued ) 



of water, we find that this inclination to a filamentous growth has pro- 

 duced an elongated form of sponge in which the excuirent openings are en 

 the sides of the long branches. 



T ese species of sponges, known as rope sponges, live prostrate on the 

 sea bottom, or climb over rocks, much as do climbing plants on the land. 

 An example of a horny sponge, but of a different genus from the rope 

 sponge, may be seen in the cord sponge (fig. 86 on the left) showing the 

 anastomosing, or joining together of two blanches. The figure to the right 

 shows a branching form of spiculigenous sponge which is common on the 

 New England coast. Another branching sponge may be seen in fig. 87, B, 

 where the forked termination is given. Beside it, at A, is an elongated form, 

 the purple sponge. A peculiar form of prostrate sponge is the creeping sponge, 

 fig. 106, where the branches have become greatly thickened. These branch- 

 es are quite large, some specimens reaching eight or ten feet in length, with 

 branches which extend several feet in diameter. 



Reproduction in Sponges. 



Sponges reproduce in two ways, sexually, by eggs, and asexual ly, b\ 

 buds. Two kinds of reproduction cells occur in sponges. Those which pro- 

 duce ova, and those which produce the male or fertilizing element ( sperm a - 

 tazoa ) The ova are fertilized within the sponge and are thus ready for de- 

 velopment when they are thrown out of the excurrent openings. Segmenta- 

 tion begins as soon as the eggs are deposited, or probably as soon as thej 



