On the connective tissues and body cavities of the Nemerteans. 27 



nerveux latéraux, qui est le lieu de formation des ovisacs et pro- 

 bablement aussi des testicules" (I can state this positively for the 

 testicles also); yet the genital products do not arise in a preformed 

 cleft or cavity, as Salensky leads us tu suppose, but first by their 

 growth within this membraneous sheath, act as a wedge which splits 

 the latter into an outer and inner layer. In other words, in a +, for 

 instance, certain cells in the connective tissue membrane above the 

 nerve chord increase in size and become ovogonia, as Salensky's 

 own figures correctly illustrate, thus cleaving the primitive membrane 

 into two layers. Accordingly, as there is no preformed cleft, it is 

 incorrect to speak of a coelom, or even of a somato- and splanchno- 

 pleura ; and the later gonadal cavity is strictly homologous with e. g. 

 the numerous small intercellular cavities in this perivisceral membrane 

 or in the basement membrane of the body epithelium, being rather 

 archicoelic than coelomic. 



To conclude: in Amphiporus, and in the other Metaneraerteans 

 examined by me, there is no primitive, coelomic cleft in the connec- 

 tive tissue sheath enveloping the nerve chords and lateral blood 

 vessels; but, by the growth and differentiation of certain of the cells 

 composing the sheath, which cells become the genital products, the 

 sheath becomes split into an outer and inner layer, these two layers 

 forming together the later gonadal membrane. The cavity of the 

 gonad arises first later, since the ovogonia (or spermatogonia) at first 

 are united into a solid intercellular syncytium. 



2)Mesenchymtissue. A body cavity persists in the adult, 

 as a metamerically constricted cavity between the intestine and the 

 proboscis sheath, as well as laterally from the latter (Fig. 33 B.C). 

 In this cavity occur a few multipolar mesenchym cells (Fig. 37), 

 similar to those of the previously described tissue, though without 

 dense intercellular substance; no free, spherical cells are found in 

 the cavity. The mesenchym cells are imbedded in a faintly staining, 

 slightly granular substance. I cannot decide from the study of 

 hardened preparations, whether this substance is freely fluid, or gela- 

 tinous in life; but the absence of floating cells in it, and its faint 

 staining power, presents a similarity to the intercellular substance of 

 the previous tissue. Certainly there is a great structural similarity 

 between the mesenchym tissue of this species and that other tissue (1), 

 their main, if not only, difference consisting in the greater density of 

 the intercellular substance in the latter. Perhaps the mesenchym 



