PLATE IV. 



The lettering is the same in all the figures. 



cu Cutieula. 

 tc Ectoderm. 

 en Endoderm. 



<j Generative organs. 



h Mesenteries. 

 im Intermediary layer. 

 m Muscle-fibres. 



vie Mesoglcea. 



ms' Upper circular muscle. 



iiifr' Lower circular muscle. 



Ova. 



r Marginal spherules. 

 sr Siphonoglyphe (cesophageal groove), 



1 Tentacles. 



All statements given as to magnifying powers have reference to Zeiss's system. 



Aulorchis paradoxa (sections through the genital tube, figs. 1-6). 



Fig. 1. Connection of an ovum with the endodermal epithelium, probably by means 

 of a thread apparatus (" Faden-Apparat"). E, Oc. 2. 



Fig. 2. Surface view of the germinal layer. I, Oc. 2. 



Fig. 3. Longitudinal section through the germinal layer. E, Oc. 2. 



Fig. 4. Transverse section through the lower part of the genital tube. A, Oc. 2. 



Fig. 5. Transverse section through the upper part of the genital tube, in the region 

 of the oral disc ; the central detritus, which is probably produced by degradation of 

 epithelium, is omitted in the drawing. A, Oc. 2. 



Fig. 6. Epithelial layer from the interior of the genital tube {cf fig. 4). E, Oc. 1. 



Fig. 7. Epizoanthiis thalamophilus ; section through the circular muscle (after 

 Erdmann). 



Fig. 8. Horizontal section through the external and the invaginated portions of the 

 body-wall of Epizoanthus thalamophilus (after Erdmann). 



Fig. 9. Hormathia delicatula. Portion of the partly invaginated body-wall cut out 

 and magnified slightly. The invaginated part bears the parietal spherules. 



