MUSEUM OF COMPARATIVE ZOOLOGY 23 



tissue cells are in direct continuation with the muscle fibres of mesen- 

 chymatous origin. From the study that I have made of the conditions in 

 Phagocata I am convinced that they are like those found in Rhabdocoeles. 

 Imbedded in the mesenchyma are the parent cells of the rhabditi and 

 also the glands that open at the surface in different regions. There are 

 two large accumulations of glands that open to the exterior, one around 

 the gonopore, the other on the ventral surface of the head region. A 

 smaller accumulation exists near the posterior end of the body. The 

 glands that occur in the head region afford important evidence of the 

 morphological equivalence of rhabditi-producing cells and ordinary 

 dermal glands. The deep ends of these glands are located behind the 

 brain, between it and the ovaries, and in passing over the brain they 

 run downward and forward till they open out on the ventral surface of 

 the head close to its anterior margin. They are numerous, and occur in 

 two bundles or groups, one on either side of the median plane of the 

 body. They appear as long sinuous tubes with enlargements or swellings 

 occurring at intervals (Plate II. Fig. 17), but without any evidence of 

 branching, and it has not been possible to distinguish between the gland 

 proper and its duct. Not being uniformly distributed, the finely gran- 

 ular contents of the tubes cause the irregular enlargements referred 

 to. Nuclei could not be detected in any portions of the ducts. The 

 two bundles of glands begin immediately in front of the ovaries, and as 

 they pass forward converge, so that when they pass over the commis- 

 sure of the brain they are in contact with each other ; but they soon 

 diverge again, and make their way to the surface as already described. 

 These two bundles of glands I believe to be the homologues of the 

 " Stabchenstrassen " found in Rhabdocoeles, and most prominently in 

 the Mesostomidse. Both the position and the course of the glands in 

 Phagocata are identical with those of the "Stabchenstrassen" in Rhabdo- 

 coeles, and the " wiederholte Anschwellungen" (A. Schneider, '73, p. 83) 

 in the latter correspond to the repeated enlargements in the former. 

 The glandular organs of Rhabdocoeles differ from them only in the 

 nature of their contents. Furthermore, the almost complete absence of 

 rhabditi in the head region of Phagocata strengthens this conclusion. 

 One has only to compare Leuckart's ('52, p. 23) description of Mesosto- 

 mum and the figures given in Graff's great monograph with the condi- 

 tions present in Phagocata, at once to recognize the probable equivalence 

 of these structures. A similar but smaller accumulation of glands is 

 found at the posterior extremity of the body in Phagocata, and it is 

 worthy of note that there is likewise in Rhabdocoeles an accumulation 



