130 



distinct in the first three to five somites, but elsewhere are obscure. 

 The number of somites is variable, the average being about 54, the 

 extremes, 46 and 58. The head pore is small and located on o/I. 

 The clitellum is on ^ XI-XIII and is usually only moderately de- 

 veloped. In the anterior region there are 3-6 setae per bundle, and 

 in the posterior region 2-4, usually 2 in the last four or five somites. 

 The arrangement of the set?e in the bundle (PI. VIII, Fig. 3) re- 

 sembles that in Fridcricia. The outer set?e of the bundle are longer 

 and heavier than the inner ones, but it should be noted that this dif- 

 ference is less than that usually found in Fridcricia. In each bundle 

 the proximal ends of the set?e are in rather close proximity to each 

 other and are arranged in transverse linear secjuence. Outside of the 

 body wall they spread out fanwise. Close examination shows that, 

 as in Fridcricia, the setae are not arranged in pairs, but represent a 

 series of different sizes. The proximal ends are distinctly bent (PI. 

 VIII, Fig. 9). 



INTERNAL CHARACTERS 



Lymphocytes. — The lymphocytes (PI. VIII, Fig. 5) are large and 

 abundant. Their distribution in the coelom is not uniform; certain 

 regions are well supplied, while other regions are almost destitute. 

 They begin to appear near IV. The space intervening between the 

 septal glands and the reproductive organs is almost completely filled 

 with them except in the region of the intestinal diverticulum, where 

 they are greatly reduced in numbers. Few if any are present in the 

 somites containing the reproductive organs, but beyond them the lym- 

 phocytes are always present although not in such numbers as in the 

 anterior parts of the body. They are disc-like or broadly elliptical. 

 The granular cytoplasm contains a conspicuous nucleus. Measure- 

 ments average as follows : length, 0.085 ""''"'''• i widtli, 0.045 ^i''"''- 



Brain. — The brain (PI. VIII, Fig. i) is in I, II, and III, chiefly 

 in II. It is somewhat heart-shaped. The posterior margin is deeply 

 emarginate and the anterior margin is decidedly concave. The lateral 

 margins converge rapidly cephalad and approach each other closest 

 at a point just posterior to the origin of the commissural nerve trunks. 

 The posterior part of the brain is approximately 2.7 times wider than 

 the anterior part. The dimensions are practically uniform, the ratio 

 of the greatest width to the greatest length being G : (). The actual 

 measurements are 0.108 mm. for the greatest width, and 0.162 mm. 

 for the greatest length. In transverse section the organ is elliptical 

 in outline. It is attached to the body wall by two pairs of supporting 

 strands which arise from its latero-posterior and ])()sterior parts. The 

 anterior part gives rise to the usual nerve trunks, which extend for- 



