REPORT ON THE TUNICATA. 



1)3 



diagrammatic form in the following figure (Fig. 10), wliiL-h shows the most essential 

 points made out by his investigations. 



Fig. 10. — Diagrammatic section of Octacnemus bijthius (after Moseley). 



b. m,irgin of basal disc ; i.a. branchial aperture; e.a. atrial aperture ; p. a. peclicle of attachment; n. nucleus; 

 (J. horizontal membrane ; r.m. radiating muscles ; r. rectum; m. mc.uth ; »;./(. nnisclcs of nucleus. 



Description of the Second Specimen, and General Remarks. 



After the curious external form, the most remarkable point in regard to Octacnemus 

 is certainly the condition of the branchial sac, in which there are evidently no apertures 

 for allowing water to pass into the peribranchial cavdty. In comparing this condition 

 with that seen in the genus Cystingia, IMoseley is probably incorrect, since there is 

 nothing in the original description of that form to lead us to suppose that there are 

 110 ojjenings in the branchial sac. As to the nature of the " horizontal membrane " 

 of the above description, I agree with Moseley that it represents part at least of the 

 branchial sac, and I would suggest that it is merely the posterior part of the ventral 

 wall of that organ, the anterior part of which has fused with the mantle. The 

 accompanying diagram (Fig. 11) represents my view as to the morphology of the 

 animal, and shows its relations to the structure of other Tunicata. 



vl'Jii 



Fig. 11.— Diagram showing the probable structure of Octacnemus. (From left side.) 

 ad. probable place of attachment ; at. atrial aperture ; at. m. membrane lining peribranchial ca\'ity ; br. branchial 

 aperture; br.s. branchial sac; end. end.' portions of endostyle ; ('. intestine; m. m.antle; n.ff. nerve ganglion; 

 n:. ft'sophagus; ov. ovary; p.bi: peribriinchial cavity ; St. stom.ach ; t. test. 



The body is apparently flattened antero-posteriorly, so that the anterior or upper 

 surface upon which the apertures are both placed is not far from the posterior or lower 

 attached side. If the o3sophageal aperture be regarded as indicating the posterior end 



