GO W. A. HERDMAN. 



Nerves, o. t. Ovo-testis. p. Pigment, r. c. Renal cavity, rh. Uhinophore 

 sph. Sphincter muscle, t. m. Transverse muscles, tn. Oral tentacles. 



Diameters. 



S. 1 = Swift's 1 in. obj.,oc. 2 .... magnifying about 45 

 S. 4 ^ ,, :f „ .... „ „ 2oU 



S. i = „ i „ .... „ „ 330 



Z. y^g- ■=■ Zeiss's -^ „ (oil immersion), oc. 2 . „ „ 505 



oc. 4 . „ 950 to 1363 



Wliere not otherwise stated, the drawings were made from specimens 

 hardened in Kleincnberg's picric acid and graduated alcohols, stained in picro- 

 carmine, embedded in paraffin, and cut with the " rocking " microtome. 



PLATE VI. 



Fig. 1. — Outline of a Doris seen from the left side, showing the rhino- 

 phores {rh.) and the brancliia3 (dr.). About natural size. 



j^iG. 2.— Part of a longitudinal section through the branchia of Doris 

 (Acanthodoris) pilosa. b. s. Large blood-space. S. i. 



Fig. 3. — Outline of Ancula cristata seen from the right side, showing 

 the rhinophores, the branchise, and the cerata (c). x 3. 



Fig. 4. — Upper part of a transverse section through the head of Ancula 

 (middle of odontophore), showing the tentacle-like branches of the rhinophores 

 (rh.) cut in longitudinal section. The mesoderm contains only a few small 

 blood-spaces (b. s.). S. 1. 



Fig. 5. — Transverse section through the front of the body of Ancula, 

 showing the rhinophores cut longitudinally, m. Muscles, n. Nerves, t/. 

 Ganglion. S, 1. 



Fig. 6. — Transverse section through Ancula at the anterior end of the 

 median branchia (br^.), showing the first pair of cerata (c^.), and the large 

 blood-space in the branchia {b. s.). S, 1. 



PLATE VII. 



Fig. 7. — Transverse section through Ancula in the middle of the median 

 branchia, and first pair of cerata. S. 1. 



Fig. 8. — Small part of median branchia in longitudinal section, showing 

 the blood-spaces in the mesoderm. S. ^. 



Fig. 9. — Small part of same branchia in tranverse section. S. i. 

 Fig. 10. — Part of the outer edge of one of the cerata shown in Fig. 7, near 

 base. S. -J-. 



