238 PROTOPLASM 



called inner capsule of the salivary gland cells of Blatta is a true 

 alveolar layer; but if so it is in any case a rather strongly 

 modified one. 



That the radially striated cuticular layer, which first 

 Sachs and later Strassburger (Zellbttdung und Zelltheilung, 2nd 

 edition, 1876) described in the Zoospores of Vaucheria, must be 

 included here, has already before been pointed out by me. I 

 estimate the thickness of this layer from Strassburger's figures 

 (1876, Protoplasma) at about 3 //,. That is rather much for an 

 ordinary alveolar layer, since its thickness depends on the width 

 of the protoplasmic meshwork, which does not as a rule con- 

 siderably exceed 1 /*. The Ciliata, however, furnish us with 

 numerous examples of similar thick alveolar layers ; in fact in 

 Bursaria truncatella it even reaches the thickness of 8 /z. There 

 can therefore be no question that this layer may be subject to 

 certain modifications, which is perhaps connected with the fact 

 that it becomes more or less rigid, and then undergoes a special 

 growth accompanied by considerable heightening of the meshes. 

 I will enter rather more closely into this question presently. 

 Strassburger without doubt gave a more correct judgment upon 

 the alveolar layer of Vauclieria originally than he did later, since 

 he at first ascribed a chambered structure to it and brought the 

 striation into relation with the radially directed walls of the 

 chambers. At a later period he gave thi& view up again, and 

 referred the striation to minute rods, for which reason he com- 

 pared the structure with the Trichocysts of Infusorians (p. 14). 

 The rods were regarded by him as essentially supporting 

 structures for the cilia. 



It was incorrect, however, when I formerly stated (1889) 

 that Strassburger had also observed a radially striated alveolar 

 layer in plasmodia. What he saw there (1876, Protoplasma) was 

 in any case only protoplasm drawn out into filaments, which in 

 the shrinking which accompanied death remained sticking to the 

 outer membrane, which was perhaps the alveolar layer. He 

 himself interprets his observations in a similar manner. 



Van Beneden (1883) figures a very beautifully developed 

 alveolar layer in the epithelial cells of the papillae at the lower- 

 end of the oviducts of Ascaris megalocephala. It is remarkable 

 that two such layers, an external lighter one and beneath that a 

 darker one, should occur. The state of things is therefore 

 similar to that in certain Ciliata (Vortwdla, see above, p. 88, and 

 Nassula), or they remind one also of the envelope together with 

 the alveolar layer in Amoeba adinopliora (Plate IV. Fig. 4), 

 Cochliopodium, and similar forms with a shell envelope resembling 

 the alveolar layer. For this reason I think that these rela- 



