iv PREFACE. 



lular structure of Aetinophrys. The relation of vitality 

 to the various degrees of organic complication. The re- 

 lation of the egg to secondary causes. Anatomy of 

 Polypi The nervous system of Infusoria. The individu- 

 ality of Hydro -Medusae, Stroliloid Medusoe, and the lower 

 Invertebrata. The peculiar mode of reproduction of the 

 hydroid genus Rhizogeton. Monstrosity and reproduction by 

 budding. The typical animal. The relation of the five 

 grand divisions to the typical animal. The typical form 

 of Protozoa and Zoopkyta. Polarity of animals. The so- 

 called radiation of Zob'phyta. A new form of ciliated 

 Infusoria, Heteromastix. The digestive system of Infusoria. 

 The longitudinal axis of Echinodermata. Anatomy of 

 the apodous holothurian, Caudina. Investigation of the 

 structure of Loligopsis, in reference to the dorsal and 

 ventral sides of Cephalopoda. The relation of the spinal 

 marrow to the vertebral axis. The development of 

 the tentacles in Tubularia. The bilaterality of Tubu- 

 laria. The structure of the scyphostoma of Aurelia. The 

 subsidiary layer of the vertebrate embryo. In this con- 

 nection the author would also request, especially of the 

 younger naturalists, the perusal of the ''Note on Scientific 

 Property" on p. 37, and also the note on p. 304. 



A large proportion of the figures which were used to 

 illustrate the lectures are reproduced in this volume ; 

 and, beside these, numerous others are introduced in 

 order to meet the requirements of the additional matter 

 and the notes. At least two thirds of these were taken 

 from the original drawings of the author, and the rest 

 were almost invariably selected from the first authori- 

 ties. In the latter case, the name of the original author 

 is given at the end of the description of the figure. 



