No. 3.] STUDIES ON CEPHALOPODS. 265 



belonging to different species would differ from each other in 

 their adult condition. Professor Weismann's phrase — " onto- 

 genetic stages of idioplasm" — aptly expresses our meaning on 

 this subject. For the metamorphoses of structures and of em- 

 bryonic tissues must of necessity correspond to the change in 

 the constituent protoplasm. Without change in the nuclear 

 substance, development is impossible ; the egg must remain an 

 ^gg forever. 



If all the determining elements of future tissues are contained 

 in the nucleus of the ovum, and if cleavage is the process by 

 which these elements are analyzed into more tangible tissues, 

 the question naturally arises as to the method of analysis em- 

 ployed in such a process. 



Such a mctJiod we find in Caryokinesis. 



I will, therefore, describe the process which may be termed 

 the mechanics of nuclear division, as based on my observations 

 on Cephalopods and Echinoderms.^ 



It is now agreed by many foremost investigators of the sub- 

 ject that the essential feature of caryokinesis Hes in the 

 division of the chromatic substance of the nucleus among the 

 daughter cells, and that the complicated system of spindle rays 

 is the mechanism to effect such a division. The development 

 of a spindle clearly shows this, and the following is an attempt 

 towards a further confirmation of the current view on the sub- 

 ject, as held especially by E. van Beneden and T. Boveri. In 

 one important respect my view is just opposite to that of these 

 authors, but this difference lies more in the interpretation of 

 phenomena than in the facts themselves. 



First of all, I will endeavor to describe the anatomy of a 

 well-developed caryokinetic figure in the Cephalopod egg, upon 

 which my observations have been chiefly carried on. The ques- 

 tion of nomenclature presents some difficulty. I will use here 

 a set of terms of a simple descriptive character, descriptive of 

 function, of origin, or of topographic relationship of different 

 parts. 



The accompanying illustration. Fig. V, shows a caryokinetic 



1 The substance of this portion has been given in my two previous notes on the 

 subject: Karyokinesis and the Cleavage of the Ovtim, Johns Hopkins Univ. Circulars, 

 April, 1890; On Caryokinesis, Biological Lectures delivered at the Marine Biological 

 Station, Wood's Holl, 1891, pp. 168-187. 



