APPENDIX. 265 



The three foregoing Tables (VI., VII., VIII.,) are in sub- 

 stance the same as Tab. I., but the differences in arrangement 

 allow some points to be brought out more clearly such as the 

 extent to which the sexual characters affect the sequence of forms. 

 Omitting the Thallogenous group of which our knowledge is 

 still too fragmentary and conjectural to allow us to generalize 

 upon it there will be seen to be a progressive increase in the 

 extent of the genetic cycle, over which this influence prevails, as 

 we rise from the lower Cryptogamia to the Phanerogamia, and 

 especially to the dioecious species of the latter. The difference of 

 manifestation is even greater than can be measured in this way, 

 as the sexual characters of the lower forms are not only more 

 limited in extent, but also of a less apparent kind fully justify- 

 ing the expressive term given by Linnaeus to the lower of the two 

 great divisions of the Vegetable Creation. 



GENETIC CYCLE IN ANIMALS. 



For the Animal Kingdom, on account of the great variety in 

 the Genetic Cycle, it would be difficult to construct convenient 

 and manageable tables arranged in parallel columns like the fore- 

 going, but I have appended in their stead tabular views of the 

 sequence of development in the families which are of most in- 

 terest in respect of their mode of propagation. 



In the following Tables (IX. -XVIII.), the division into 

 columns indicates the existence of sexual distinctions in that 

 part of the cycle where it occurs the left-hand column giving 

 the spermatic, and the right, the germinal structures. Unless 

 contra-indicated by the punctuation, the reading is to be carried 

 across the page. The horizontal lines indicate a breach in the 

 continuity of structure. This may sometimes affect only one 

 sex, as in the detachment of the spermatozoa of animals gene- 

 rally, while the ovum is commonly impregnated, and often 

 incubated, within the body of the female. 



Brackets are used to imply that the parts or processes men- 

 tioned are only of occasional occurrence in the group. 



