No. 6.] DEVELOPMEA\"F OF PARYPHA CROCK, I. 303 



embryological development, being very numerous in the enclo- 

 derm of the young hydroid when it escapes from the gonophore. 

 Isolated ones are even found in the endoderm of the tentacles, 

 as noted by Doflein, but I cannot agree with him that they are 

 entirely confined to that layer. 



Segmentation of tJic Ovum. 



The egg, after assuming the typical form already described, 

 goes into a resting stage, as a large number are found in that 

 condition and without nuclei. Soon, however, an irregular 

 mass of nuclear matter appears at one pole. Sometimes this 

 forms a single mass, in other cases it is made up of two or 

 three more or less isolated portions. Whether these are finally 

 assembled to form a single nucleus, or whether two or three 

 nuclei are thus produced, I am unable to say, as many of the 

 sections in the later stages might be interpreted either way. 

 In some of the eggs a single definite star-shaped nucleus was 

 present, but in others there were two, and in one case four of 

 these nuclei lying close together at one pole of the egg. There 

 was nothing in these eggs to indicate that the nuclei had not 

 been derived from a single nucleus, but, on the other hand, 

 some of the disorganized masses of nucleoplasm could not but 

 give the impression that more than one would be formed. 

 However, the number is of minor importance, and the real 

 interest attaches to the fact that such a reorganization occurs 

 at all. That it does, I am fully convinced. I have examined a 

 large number of sections with this question particularly in my 

 mind, and am forced to the conclusion that the nucleus of the 

 mature egg is formed by the reorganization of the fragments of 

 the nuclear matter scattered through the cytoplasm. 



The earliest stage in which definite mitosis was observed 

 was in the egg shown in PL III, Fig. i. In this three definite 

 nuclei, one in a process of division, showed in a single section. 

 Another section through the same egg revealed a fourth nu- 

 cleus which, from its position, might have been derived from 

 one of the others, but no spindles were observed. There were 

 no signs whatever of segmentation planes in this egg. The 

 development in the eggs of Parypha is very irregular indeed, 



