Xo. 3. — On some Points in the Anatomy and Histology of 

 Sipunculus nuclus, L. By Henry B. Ward. 1 



I Introduction 



Methods 



II. External Anatomy .... 



1. Introvert 



2. Tentacular Fold .... 

 III. Histology 



1. Body Wall 



a. Cuticula and Hypodermis 



b. Cutis 



c. Pigment Cells .... 



d. Dermal Bodies .... 

 a. Bicellular Glands . . 

 p. Multicellular Glands . 

 ■y. Sense Papillae . . . 



e. Muscular Layers . . . 



Contents. 



Page 



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IV. 



2. Tentacular Fold . . 



a. Oral Wall .... 



b. Migratory Corpuscles 



c. Musculature . . . 



d. Vascular System . 



e. Aboral Wall . . . 



3. Nervous System . . 



a. Brain 



a. Ganglionic Cells 

 p. Internal Structure 



b. Cerebral Nerves . 



c. Ventral Nerve Cord and 

 Plexi 



4. Cerebral Organ . . 

 Conclusions 



Bibliography 180 | Explanation of Figures 



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183 



I. Introduction. 



Some two years ago, while working on Sipunculus nudus in the zoo- 

 logical laboratory at Gottingen under Prof. E. Ehlers, my attention was 

 attracted by a peculiar organ in the region of the dorsal ganglion ; and 

 although it was a prominent feature of all transverse sections, no men- 

 tion of its presence was found in the literature on Sipunculus. The ob- 

 servations made at that time interested me so much that the opportunity 

 afforded by a short stay at the Xaples Zoological Station last spring, 

 for which I am indebted to the great kindness of Prof. A. Weismann and 

 the Cultusministerium of Baden, was embraced to procure new, carefully 

 preserved material. A study of the literature on Sipunculus revealed 

 such lack of agreement between authors that a more general studv 

 of the form seemed likely to yield results, and, on the advice of Prof. 



1 Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology, under the direction of E L. Mark, No. XXVI. 

 vol. xxi. — no. 3. 



