ON LAFG3A DISPOLIAN^ SP. N. 109 



the host where the greater part of the cosnosarc lies, and 

 opposite to the hydrocauline cavity. The parasite is shut ol¥ 

 from the coeiiosarc of the host by a layer of perisarc {p. H.) 

 which is continuous with a layer running- partly round the 

 inside of the Sertularian tube. It is clear that the growing- 

 apex of the parasite forces itself into the coenosarc of the 

 host, which responds by secreting a partition separating it 

 from the invading Laf oea. In fig. o the parasite has grown 

 away from the perisarc tube of the host into the middle of 

 the ectodei"m of the coenosarc, and the Sertularia has 

 secreted a continuous tube of perisarc (^J. H.) around the 

 parasite. Fig. 2 represents an intermediate condition between 

 that seen in fig. 1 and fig. 3. 



Within the host the parasite secretes practically no parisarc, 

 but it may be represented by the thinnest possible layer as at 

 p. P., figs. 4 and 6. 



Thus, in Text-tigs. 1 and 2 what looks like the perisarc of 

 the Laf oea is really a tube of chitin secreted by the host to 

 shut off the parasite. Outside of the host the hydrorhiza of 

 the Lafoea assumes greater dimensions than inside, as at 

 P. 0., figs. 1-3. 



In fig. 4 the cross-section shows the Sertularian hydrotlieca3 

 of the two sides. On the left the hydrorhiza-sac {li. s.) of the 

 parasite, adhering to the adcauline surface, is seen, and on the 

 right side in addition to the sac a transverse section of the 

 base of the Lafoea {h. H.) polyp is present. 



In fig. 5 the cross-section shows the parasite passing 

 through the lower opening of the hydrotheca, and it is still 

 separated from the ectoderm of the host by a partition of 

 perisarc [p.H.). It would appear that only in the region of 

 the growing apex of the parasite does the living tissue of 

 parasite and host remain in contact. 



In fig. 6 the junction of the base of the polyp {h. E.) and 

 the hydroi*hiza-sac [h. s.) is seen. 



In fig. 7 there is shown under greater magnification the 

 coenosarc of the Sertularia, containing the hydrorhiza of the 

 parasite encircled by a tube of perisarc secreted by the 



