On the conucctive tissues and body cavities of tJie NeinertoRiis. 15 



wall away from the surrouiuling gelatinous tissue." Büüoeu's ('90) 

 results arc more in accord with mine, since he states, of a s[)lit 

 found between the intestine and the "parenchym": "In der That, es 

 gelingt bei Cerébratulus marginatus sowohl einen Kernbelag nach 

 aussen auf dem Pareucliym, der sich einer feinen Haut anlegt, fest- 

 zustellen, als auch am Darmtractus einen solchen statt einer fibrösen 

 Substanz, welche Salensky hier beschreibt, zu constatiren" (p. 62). 

 But no author has thus far described the true mesenchym tissue oc- 

 cupying this space, which is probably to be accounted for by their 

 use of poor fixing reagents. 



In the immature Cerehratulus lacteus I find a spacious body 

 cavity, situated between the intestine and the inner longitudinal muscle 

 layer, thus surrounding the nephridia and blood vessels (Figs. 19 a 

 — c B.C). This cavity begins a little anterior to the mouth, and 

 continues backward, being most spacious in the region of the posterior 

 intestine, to the caudicle {miJii = "caudal papilla" Hubrecht, 

 = "Schwänzchen" Bîjrger), where it becomes nearly obliterated by 

 the massing of mesenchym cells. I will leave to a future time the 

 consideration of the morphological equivalence of this cavity, which 

 may represent a pseudocoel, or a combination of pseudocoel and 

 coelom. 



In the structureless, unstaining fluid of this body cavity are 

 situated the mesenchym cells. These are elongated, bipolar, seldom 

 multipolar cells, with irregularly flattened, branching and anastomosing 

 fibres, which produce a loose cellular network in the body cavity 

 (Fig. 20, Figs. 19 a— c. Mes). They are, further, membraneless, and 

 generate no intercellular substance. The caudicle excluded, these 

 cells occupy but a small space in the body cavity, being found most 

 abundantly between the body muscular wall and the blood vessels, 

 thus supporting the latter, and also between the muscular wall and 

 the intestine; further, they occur quite abundantly above the oeso- 

 phagus, and around the posterior portion of the cephalic vascular 

 lacunae. The nucleus of each cell stains deeply with haematoxylin, 

 and is usually spherical, and on account of its form is to be easily 

 distinguished from the elongate nuclei of the connective tissue pre- 

 viously described. It is situated near the middle of the cell, the 

 finely alveolar cytoplasm of which completely enve]oi)S it. 



A discontinuous layer of mesenchym cells, which are held in 

 mutual connection by the anastomosing of their fibres, is found as a 

 lining of the inner surface of the inner longitudinal muscle layer of 



