No. 3.] 



STUDIES ON CEPHALOPODS. 



263 



fertilized ovum contains all the hereditary characteristics of 

 the parent organism. It is this structure in the ovum which 

 stamps the particular characteristics upon an organism of a 

 given species. The study of fertilization has clearly demon- 

 strated the metamorphosis of the sperm-nucleus into a constit- 

 uent part of the cleavage-nucleus, and thence it is distributed 

 to all nuclei formed in the subsequent cleavages. Morphologi- 

 cally, all the hereditary characteristics which the infant organ- 

 isms inherit from the par- • ■ . 

 ents, must be traced back 

 to a certain number of 

 chromosomes which come 

 from the sperm and egg- 

 nuclei of the fertilized 

 ovum. By cleavage, the 

 potential characteristics . 

 become gradually analyzed • 

 into their special attributes • ^ 

 — the attributes which we 

 assisrn to different tissues 

 of the larval or the adult p- 

 organism. If, therefore, I 

 may use one word to charac- 

 terize the whole process of 

 cleavage of the ovum, the 

 term Analysis will perhaps 

 best express our interpreta- 

 tion of the phenomenon. 

 It is true that we know 

 very little as to the essen- 



M^ 



Figure V. — Loligo. 



tial respects in which the nuclear substance in the entodermic 

 cleavage sphere differs from the similar substance in the ecto- 

 dermic sphere. In the present state of our knowledge on this 

 subject, we can only infer a structural difference of the pro- 

 toplasm from the careful study of the fate of the respective seg- 

 ments. If, for instance, one cell gives rise to a sense-organ, the 

 fundamental molecular structure of that cell must be different 

 from another which contains all the germs of an excretory 

 organ, just as we are forced to conclude that the ova of differ- 

 ent organisms are of necessity different, even if they appear 



