EARTHWORM PHARYXX EPITHELIUM. 215 



wall, in or near the median plane, and extending from the seventh 

 segment forward to the third. The remainder of the operation 

 was performed under a compound dissecting microscope. Very 

 fine oculists' scissors were used. The body wall was pinned back, 

 exposing the cephalic ganglia lying just above the pharynx in the 

 third segment. With dissecting needles the ganglia could be raised 

 from the tissue below and then snipped off at either side. The 

 operation offered considerable difficulty, so that sometimes a part 

 of either connective with the heavy nerve which runs to the pha- 

 rynx wall was removed. When this happened it was impossible 

 to tell whether or not the pharynx was injured, but it is very likely 

 that it was. Therefore, to obviate possible injury to the dorsal 

 region of the pharynx wall, and in order that the epidermal wound 

 be as remote as possible from the expected (dorsal) site of the 

 brain anlage, the operation was in some cases modified by making 

 the incision dorso-laterally or even sometimes ventro-laterally. 



Operations of the kind described above were performed on about 

 eighty worms. The species Allolobophora fcetida was used be- 

 cause of its capacity for quick regeneration. At various stages the 

 operated worms were fixed in Bouin's picro-formalin, the anterior 

 ends cut transversely, and the sections stained with hsematein-eosin. 

 The following description is based on a careful study of twenty- 

 five cases. 



To insure appreciation of conditions in the operated animals, 

 reference must be made to certain features of the brain region of 

 the normal earthworm. Fig. i represents diagrammatically a typi- 

 cal cross-section through the brain region of the normal worm. 

 The epidermis (e) consists of fairly large columnar cells having 

 oval nuclei each containing a prominent nucleolus, and among these 

 cells are numerous large gland cells. Beneath the epidermis is the 

 body- wall muscle (outer circular and inner longitudinal fibers) and 

 between the inner muscle layer and cephalic ganglia (br.) is a 

 space containing some connective tissue and blood vessels (bl.v.}. 

 Around the brain is a distinct connective tissue sheath (c.t.s.}. 

 The periphery of the brain tissue is largely made up of typical 

 pear-shaped nerve cells, while the central mass is mainly fibrillar. 

 Continuing from the brain downward around the pharynx, to 

 which they send off heavy nerves (p.n.) on either side, the circum- 



