STRUCTURE AND ni':VF.UnpT\Tl',NT OF COFJ.OPT-ANA. 39 



('04). This author has asserted that, the sexual cells take their origin 

 in the mesodermal gelatinous tissue and migrate into the endoderm, 

 where they undergo development and maturation. Mortf.xsf.n, more 

 recently ('12), based upon his study in Tjalficlla, expressed his opinion 

 in favour of the endoderm hypothesis. 



Now, m}- observation in Cocloplana has ascertained that, the 

 sexual cells of either sex make their appearance in the basal part of 

 the endoderm of the canals representing the meridional canals of ordinary 

 ctenophores. However, the observation falls short of proving whether 

 or not the migration of the cells such as assumed by Schneider does 

 take place. But so much it may be said as certain that, if the migra- 

 tion occurs, it would be in some very early stage of the development 

 of the cells, when these are still very small and extremely hard, if 

 not altogether impossible, to recognize from the other kinds of cells in 

 the body parenchyme. Anywa\', it is certain that, contary to Hertwig's 

 view, the sexual cells pass most of their lives in the endoderm. That 

 view Hertwig's is based upon his observations on a cydippid, Callianira, 

 which has some flask-like invaginations along each meridional canal, 

 at the base of peculiar wing-shaped processes of the aboral pole of the 

 bod)^ He has given the invaginations the name of " Genitalsackchen ", 

 upon the assumption that the cells lining their terminal part would 

 undergo multiplication and give rise to gonads. This hypothesis was 

 supported further by the existence of certain cell strands that stretch 

 between the epidermis and the enveloping membrane of the gonads. 

 Each of these strands, called by him " Verbindungsstang ", should be 

 transformed from the neck portion of the Genitalsackchen by complete 

 obliteration of the internal lumen, except in the terminal part where it 

 persists as the genital sinus. Against this assumption Hertwig's, Chun 

 ('92) has objected, in the first place, that, the invaginations occur in no 

 ctenophore other than Callimiira, and even in this form are absent from 

 the oral parts of the meridional canals whence also develop gonads; 

 in the second place that, the invaginations show no variation with 

 respect to their situation and number between quite young and fairly 

 old individuals; in the third place that, the neck portion never undergoes 

 such a change as assumed by Hertwig, moreover, they differ greatly 

 in their histological features from the ovary; and lastly, even if the 

 development of the ovary could be explained in this way, there remains 

 to be answered the question on the origin of the testis. These objections 

 are, in my opinion, all of great importance, and this is especially so as 



