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5. Some Disputed Points in the Anatomy of the Limpets. 



Bv M. A. Willcox, Ph.D., Prof, of Zoology in Wellesley College, Welleslev, 



Mass., U.S.A. 



(Abstract of a paper read before the American Morphological Society, 

 December 1900.) 



eingeg. 26. Juli 19U1. 



The three points to which reference is made in this paper are the 

 right, or large, nephridiiim, the coelom and the subradular organ. The 

 species upon which 1 have worked is Acmaea testudinalis Müller; 

 of this animal I have had abundant material both living and preser- 

 ved in various ways. With these advantages it has been possible to 

 settle some points hitherto in dispute. 



Nephridium. In a previous paper I have described the nephridium 

 in another species of Acmaea as having much the same form and ex- 

 tent as in Patella, being a large sac beset, especially in the anterior 

 part, with numerous out-pocketings, enwrapping the viscera on the 

 right side and behind and sending forward on the left side a dorsal 

 branch which extends to the pericardium (Cf. Willcox, Jena. Zeitschr. 

 Bd. 32. p. 439 — 441). These conclusions having been challenged by 

 Haller (Zool. Anz. Bd. 33. p. 62), I have recently undertaken a study 

 of the fresh organ, with especial reference to the character of its epi- 

 thelium. This is undoubtedly of a secretory nature. The cells vary in 

 shape from cubical to columnar, are beset with long and very delicate 

 cilia and are laden with dark green granules which render the entire 

 organ very conspicuous and prevent the possibility of a mistake as to 

 its extent. Such cells have already been described by R. Ferri er 

 (Ann. d. Sciences nat. (7.), T. 8. p. 143) as the primitive nephridial cells 

 of the Gasteropoda. The right nephridium in the two species of 

 Acmaea which 1 have studied is similar to that of Patella and presents 

 no extraordinarily primitive features. If we may draw an inference 

 from these forms regarding Lottia [Acmaea] virklula, the form studied 

 and figured by Haller, we must conclude that he is in error in de- 

 scribing the right nephridium as a small sac occupying the right an- 

 terior part of the body and opening posteriorly into the large coelom. 

 The greater part of what he considers coelom is indubitably nephridium. 



Coelom. Between the ventral face of the viscera on the left side 

 and the underlying muscle is a space whose interpretation has given 

 rise to much dispute. Haller believes it a part of his coelom, sepa- 

 rated from the right half (which is in reality a part of the nephridium) 

 by an imperfect septum. Pelseneer in a paper quoted by Haller but 

 which I have not yet been able to see states that he considers it a true 



