MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 133 



the glandti, although the portion to be drawn was chosen at random. In a few plates in ni}- 

 sections of the glandular portion of the organ I have seen the ends of the sensory cells project- 

 ing- beyond the surface of the epithelium as sensory spikes, but in most places the projecting 

 parts wore not present. Whether this is the normal condition or is due to poor preservation of 

 the material I can not say. 



The nerves (Fig. 8, N) which enter each side of Van der Hoeven's organ end in ganglia at 

 the sides and near the posterior ends of the lamiuffi (Fig. 41,35; Fig. (36, Gn). From the gan- 

 glia a small nerve extends into each lamina (Fig. 66, N), and two or three nerves on each side 

 pass into the posterior glandular region. Each nerve to the laminse is accompanied by a small 

 artery. The laminar nerves possess an outer la_yer of ganglion cells as well as ganglion cells 

 scattered throughout them. Each of the small lobular divisions of the anterior part of the organ 

 receives a single nerve as well as the thin laminae. 



The facts described seem to me to constitute good and sufficient evidence for considering the 

 inferior labial lobe of the female and Van der Hoeven's organ to be homologous. The position 

 in the body is the same; the principal muscles are very nearly alike; the innervation is the same; 

 the course of their blood vessels is the same. 



It also seems probable that each lamina corresponds to one of the cirri or lamellte borne upon 

 the inferior labial lobe of the female. The main evidence for this rests upon the innervation of 

 the lamina?, which is exactly similar to that of the cirri and lamellae of the inferior labial lobe. 

 The structure of the nerves themselves is also the same in the two organs. The presence of a 

 small blood vessel running close to each laminar nerve also constitutes a bit of evidence in favor 

 of this view. The number of laminffi in Van der Hoeven's organ is the same as the number of 

 cirri and lamella? combined of the inferior labial lobe, and the reasons for considering the cirri 

 and lamellffi of the latter to be homologous have already been brought forward. 



Finalh' the sensory cells add support to the view. It will be remembered that between the 

 lamella? of the inferior labial lobe are pits lined by a peculiar epithelium. The cells of this 

 epithelium appear to be exactly similar to the sensory cells scattered over the surfaces of Van 

 DER Hoeven's organ, and I think it not improbable, taking into consideration the other evidence 

 for the homology of these organs, that during the course of the metamorphosis of the inferior 

 labial lobe of the male, the sensory cells, which in the female are confined to limited areas occu- 

 pied by them alone, have become distributed over the entire surface of the organ. 



The glandular part of Van der Hoeven's organ, which forms so large a proportion of the 

 whole, does not seem to correspond to any portion of the inferior labial lobe of the female. The 

 gland is probably a new formation developed in accordance with the changed and special func- 

 tions of the lobe. 



The inferior labial lol)e of the female is evidently in much more neaidy the primitive condi- 

 tion, its parts being but little modified from the type of structure of the many simple tentacles 

 around it. 



Here, too, the question constantly arises, What are the functions of this organ? 



When any organ dift'ers so much in the two sexes it seems only reasonable to consider that 

 it is a sexual organ of some sort. We have, then, at least reasonable grounds for saying that 

 Van der Hoeven's organ, and possibly the inferior labial lobe, is an accessory sexual organ; 

 but we know nothing whatever of its chief functions. Apparently its secretory functions are 

 only periodically and not constantly active. To what use the secretion is put is impossible to 

 guess, even if guesses happened to be desirable. The organ may be a sensorj- organ all the 

 time and a secretory organ only part of the time, or both functions may be active only period- 

 ically. In the latter case, again, the sensory function may be active only when the organ is not 

 secreting, or this may be the time when the sensory function is most active, or the only time 

 when it is active. It seems prol)able that the sensory function is either that of tasting or smell- 

 ing. Possibly the activity of the secretory cells, or at least the flow of secretion, depends upon 

 the perception of certain substances in the water by the sensory cells, or the sensorj' function 

 may have a much closer relation to the everyday life of the animal. 



