Carter, and any one can with patience and care observe the life 

 history of the marine sponges. 



It seems, then, that the life history of the sponges consists of 

 the following stages : — 



1. Fertilization of a true egg by genuine spermatozoa; both 

 eggs and sperm cells arising from the inner germ-layer. 



2. Total segmentation of the yolk, or protoplasmic contents of 



3. A ciliated embryo. 



4. A free swimming " planula "-like larva, with two germ-layers, 

 not, however, originating as in the true planula of the acalephs. 

 The planula becomes sessile, spicules are developed in the hinder 

 end of the body, afterwards a gastro-vascnlar cavity appears, 

 constituting the 



5. Gastrula stage. 



6. A mouth and side openings appear and the true sponge char- 



REVIEWS AND BOOK NOTICES. 



an octavo volume of two hundred and seventy pages, with three 

 plates. Beginning with the Araneae he describes the Epeiridae, 

 Uloborida?, Dictynidae, Enyoidffi and Pholcidas. This arrange- 



the work on these families was first finished by the author. The 

 introduction is promised in a future part, but the present volume 

 begins with a short review of the principal descriptive works on 



