104 DE. J. STEPHENSON ON TEE MORPHOLOGY, CLASSIFICATION, 



The classification of the Megascolecidse, to which both sub- 

 families, the Octochsetina? and Trigasfcrinae, belong, proceeds on 

 phylogenetic lines ; and a very considerable degree of success has 

 been reached in the filiation, and consequently in the definition 

 and arrangement of genera. The origin of the family, as is now 

 generally recoguized, is to be sought in the " original Acantho- 

 driline," a form which is represented at the present day by the 

 genus Notiodrilus as defined by Michaelsen in the Tierreich 

 volume (1). Its essential characters (for our present purpose) are 

 as follows : A pair of male pores on xviii., two pairs of prostates 

 opening separately on xvii. and xix., a single oesophageal gizzard, 

 four pairs of setaa per segment, one pair of meganephridia per 

 segment, no calciferous glands. 



The important, characters of the genera which enter into the 

 following discussion may be stated thus : — 



Diplocardia, one remove from the original Acanthodriline, and 

 the ancestor of the Trigastrinse, differs from the original Acan- 

 thodriline only in having two gizzards. It is found in North 

 and Central America. 



Trigaster, descended from Diplocardia, differs from the latter 

 genus in being micronephridial ; the posterior male organs are 

 either of the acanthodriline type or they may have undergone 

 the " microscolecine reduction " (disappearance of the posterior 

 pair of prostates, and union of the male pores with the anterior 

 prostatic openings on xvii.) ; there are two or three gizzards, but 

 no calciferous glands. Trigaster is found in Mexico and the 

 West Indies. 



Dichogaster is similar to Trigaster, except that there are 

 calciferous glands in two or three of the segments xiv.-xvii. A 

 point to which attention has been called is that while in Trigaster 

 the setal interval cd is greater than ab, in Dichogaster these 

 intervals are approximately equal. Eudichogaster was supposed 

 to resemble Trigaster in this respect, but in a few species ab is 

 equal to cd. Dichogaster is endemic in tropical Africa, and 

 probably in Central America and the West Indies, but has spread 

 widely in the tropics and warmer temperate zones. 



The first development, therefore, in the above line of descent 

 (Diplocardia- Trigaster-Dichogaster), and the primary charac- 

 teristic of the Trigastrinaa (I include Diplocardia in the 

 Trigastrinse, v. post.), is the reduplication of the gizzard. 



The genus Octochaitus belongs to a different line. It differs 

 from the original Acanthodriline in being micronephridial, and 

 in having a pair of calciferous glands in segment xv. or xvi. (a 

 few species, to which more particular reference is made subse- 

 quently, are without calciferous glands); it has the single gizzard 

 and other characters of the ancestral form. It occurs in India 

 and New Zealand. 



The other genera of the subfamily need not be mentioned here. 

 The first development in the Octochartinse, and therefore their 



