262 SOME RECENT 



Kleinenberg, in 1878, published an account of 

 the early stages of development of an earthworm, 

 Lumbncus trapezoides, which he obtained abun- 

 dantly in the gardens of the island of Ischia. The 

 worms lay their eggs in capsules : each capsule is 

 from one to eight millimetres in length, and is 

 filled with an albuminous mass in which are 

 contained bundles of ripe spermatozoa, and from 

 three to eight eggs. Of the eggs only one 

 develops as a rule, the remainder gradually dis- 

 appearing. At an early stage in development, as 

 soon as the germinal layers are established, and 

 before the appearance of any of the organs or 

 parts of the embryo, the ovum divides into two 

 parts which are usually equal and similar. Each 

 oT these parts develops into an embryo, and sub- 

 sequently into an adult worm ; the two remaining 

 for a time connected together like Siamese twins, 

 but ultimately separating. 



The upshot of the process is that what Haeckel 

 effected artificially for Crystallodes i.e., the division 

 of the segmented egg into two parts each of which 

 develops into an embryo is found to be a natural 

 or even normal occurrence in Lumbricus trapezoides. 

 Kleinenberg supposed that the tendency to form 

 twins, which is so marked a feature in Lumbricus 

 trapezoides, was due to a process of double fertilis- 

 ation, two spermatozoa instead of one being con- 

 cerned in the act. Vejdovsky however suggested 

 that the twinning was perhaps influenced by warmth, 

 for it occurred most frequently in warm weather ; a 

 suggestion which receives much support from some 



