146 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



' reducing division' of the germ-cells, is not confined to Pyrrho- 

 coris ; for Flemming long ago described an entirel}'^ similar 

 ring-like structure in the salamander, and my assistant, Dr. 

 Hacker, has recently observed the formation of wreaths of 

 idioplasm in the egg-mother-cells of certain Copepoda. The 

 development of these latter does not, however, altogether agree 

 with that of the wreaths of Pyrrhocoris, although the same 

 purpose is served — viz. the arrangement of the ids in fresh 

 groups. 



■ 



Objections. 



The objection may be raised to my interpretation of the 

 processes of maturation in Ascaris, that, although it corresponds 

 sufficientl}'' well with the variety hivalens and with all other 

 animals possessing four or more idants, it does not apply to 

 those with only two, such as the variety iinivalens. When the 

 mother-cells contain only two idants, the mature germ-cells 

 contain only one, and hence it is a matter of indifference whether 

 the ' reducing divisions ' are preceded by the doubling of the 

 idants or not. It might be m.aintained that this doubling and 

 the consequent necessity for two divisions, are not explained 

 b}^ my interpretation. 



For this variety of Ascaris megalocephala, the objection is 

 certainly valid ; but the question arises whether this is by 

 itself sufficient to undermine the whole attempt at explanation. 



In the first place, in no other living being have so small 

 a number of idants been found as in this variety of Ascaris 

 megalocephala. Even so few as four idants occur but rarely : 

 and in the nearest relatives of the species, for instance in 

 Ascaris htmbricoides, twelve: idants are found ; in other Nema- 

 todes, according to Carnoy, there are eight to sixteen ; in Sagitta, 

 according to Boveri, eighteen ; and the same number in Echinus ; 

 in a Medusa, Tiara, twenty-eight ; and in three diiferent genera 

 of molluscs thirty-two. Ascaris m. tinivalens is in this respect 

 an exception, and should perhaps be dealt w^ith from this point 

 of view, especially as the variety bivalens, with four idants, 

 appears to be the more common. We know nothing about the 

 phenomena of heredity in this parasite of the horse, and cannot 

 decide whether the descendants of the variety bivalens are not 



