Dr. W. Michaelsen on the EnchytvEeidee. 421 



mirabilis (fig. 3 h) and M. primcevus it is tliick, with irregu- 

 lar and often strong dilatations, and is multicellular in trans- 

 verse section. In M. falciformis^ M. Beumeri (fig. 1 e), and 

 M. Jlavidus it is thinner, nearly smooth, with only slight 

 dilatations, and exhibits only a few cells in transverse section. 

 I have found a similar cardiac body in no other Enchytrseid. 

 It must probably be regarded as an ingrowth of the intestinal 

 epithelium into the dorsal vessel, and therefore as homologous 

 with certain organs in other Enchytrseidge, such as the intes- 

 tinal diverticulum of the Buchholzice. 



The cerebrum of the Mesenchytrcei (figs. 1 c and 2 h) is 

 straightly truncated or only slightly concave behind. In 

 front it is more or less deeply emarginate, and upon the 

 anterior branches, which pass over into the commissures, the 

 coating of ganglion-cells extends far forwards, even to the spot 

 where the cephalic nerves branch ofi". Two pairs of muscles 

 are attached to the cerebrum, one on the upper surface (figs. 

 1 c and 2 b, om)y the other below (figs. 1 c and 2 3, um). At 

 the posterior angles, and leaving these between them, they 

 go oif from the brain obliquely backwards, nearly parallel to 

 each other. The segmental organs also exhibit an exceed- 

 ingly characteristic development (see figs. 1 (f, 2 c, and 8 a). 

 They consist of a minute, funnel-shaped, anteseptale, and a 

 large, remarkably irregular postseptaie, usually furnished with 

 lobate or capitate excrescences. A relatively wide vibratile 

 canal traverses the anteseptale in a straight line ; but in the 

 postseptaie it is so much twisted and so closely entwined 

 that here the enveloping cell-substance is reduced nearly to a 

 minimum. The irregular excrescences of the segmental 

 organs have nearly the appearance of hernioidal diverticula 

 of the vibratile canal. In Eisen's figures this characteristic 

 course of the vibratile canal is not to be recognized ; but in 

 this respect his species do not differ from the German ones. 

 From fig. 3 a, which is the exact representation of a tano-en- 

 tial section through a segmental organ of M. mirabilis, it will 

 be seen that Eisen (2, fig. 25) has represented the vibratile 

 canal as much too spacious, so that these peculiar structural 

 conditions have not been expressed. This applies also to the 

 figures of the segmental organs of M. jorimcevus and M. falci- 

 formis (2, figs. 24 and 26). 



Finally, the sexual organs of the Mesenchytr-cei a\&Q exhibit 

 peculiarities. The seminal ducts are short, at the utmost 

 eight times as long as the seminal funnel. The spermatozoa 

 and ova fall into the body-cavity before they have reached 

 maturity, but they do not then float freely about in it. For 

 their reception more or less deep, tubular, or sacciform poste- 



