20 BULLETIN OF THE 



such a nature that sensory organs would still be of great importance in 

 the animal's economy. 



To summarize, then, the dermal rods are to be considered as condensed 

 secretions arising in sub-hypodermal unicellular glands of ectodermic origin. 

 All gradations exist between rhabditi and the secretions of normal glands. 

 Tlie rhabditi are being continually cast out of the body, and replaced by new 

 ones developed in new parent cells within the body parenchyma. The con- 

 nection of the parent cells with the epidermis is a primitive one, and the 

 rods pass to the exterior by means of the tubular ducts formed by the neck 

 of the elongated cells. The rods lie between the cells of the epidermis; they 

 are slotvly soluble in water, and are used by the animal in securing food 

 and for protection. 



The basement membrane is a homogeneous layer immediately under the 

 hypodermis, the cells of which are directly connected with it. It varies 

 in thickness in different individuals and in different parts of the same 

 individual ; 1 p. and C.5 jx are the extremes that I have found. It 

 stains deeply in all of the carmine dyes, and always takes a darker color 

 than the underlying muscles. A granular condition, such as is men- 

 tioned by Iijima ('Si, p. 375), does not exist, nor is there any appear- 

 ance of the fibrous structure described by Lang ('84, p. G3) for Polyclads. 

 Minot ('77, p. 408) states that the basement membrane is composed of 

 circular fibres. The only appearance in Phagocata approaching that 

 described by Minot is seen in surface views of bits of the membrane 

 occurring in isolation preparations, where on one surface there appear 

 parallel markings ; but these are no doubt due to the intimate contact 

 of the membrane with the circular muscle fibres. The membrane is 

 closely applied to the muscle fibres, and in longitudinal sections, where 

 the circular muscles are cut across, the inner contour appears uneven, 

 owing to the projecting ridges which it sends, into the intermuscular 

 spaces (Figs. 4, 6, 7, and 10) ; stated in another way, the circular mus- 

 cles may be said to indent the basement membrane, leaving their 

 impression in the form of parallel grooves on its under surface. In 

 cross sections of the worm, the inner border of the membrane appears 

 perfectly smooth, and parallel to the circular muscles (Fig. 2). The 

 only departure from homogeneity is caused by the fine channels occupied 

 by the processes of the parent cells of the rhabditi (Figs. 1, 4, 6, 7, and 

 10), and these are only transitory, soon becoming obliterated. Occa- 

 sionally pigment granules find their way through these openings, and 

 may become caught in the basement membrane. 



