563 



On the dorsal side one finds a pair of otocysts (statocysts). These 

 are relatively small and very inconspicuous as compared with those of 

 Lingula of the same stage. In Discinisca they are situated outside the 

 anterior occlusor, while in Lingula they are found posterior to the muscle. 

 In both forms they are imbedded in the gastro-parietal bands. In Dis- 

 cinisca they must become smaller at the time of attachment, since, during 

 the swimming stages they are of considerable size. Moreover, Fritz 

 Mil 11 er 3 studied the process of reduction of this organ at the time of 

 attachment. In older larvae he failed to demonstrate its presence. Longi- 

 tudinal sections of the largest specimen available (4 mm in shell-length), 

 show, however, one of the otocysts fairly large and containing seventeen 

 otoliths (Fig. 2 ot). The thickness of the shell makes it impossible to 

 see the otocysts before sectioning. It is, therefore, difficult to decide 

 whether they persist throughout life or not, until a careful study of the 

 gastro-parietal band of the adult Discinisca is made. 



I have elswhere expressed the opinion that the Discinisca larvae 

 may attach themselves soon after the four-pair-cirri stage, basing it upon 

 the fact that swimming larvae older than those with four pairs of cirri 

 had not, up to that time, been obtained, and upon the observation made 

 by Fritz Müller that the fixation of the larvae to the substratum takes 

 place after five or six day's confinement (1. c. p. 107). This surmise is 

 now verified; for I have at present an attached specimen with six pairs of 

 cirri. We may, therefore, conclude that in Discinisca the swimming life 

 comes to an end somewhere at the five-pair-cirri stage, that is, much 

 earlier thsin Lingula: since the latter fixes itself at the ten-pair-cirri stage. 

 I say earlier, because it is quite probable that the addition of new cirri 

 takes place at the same rate in both forms. In this connection, it should 

 be noted that in Discinisca there may exist a close correlation between 

 the early attachment of the larvae and thejprecocious diminution in size 

 of the statocysts. 



Zoological Laboratory, Columbia University, New York. September 30. 1905. 



2. Beobachtungen über die wachsabscheidenden Organe bei den Hummeln, 

 nebst Bemerkungen über'die homologen Organe bei Trigonen. 



Von Dr. L. Dreyling. 



(Aus dem Zoologischen Institut in Marburg.) 



(Mit 6 Figuren.)] 



eingeg. 2. November 1905. 



I. Hummeln. 



In Nr. 708, Bd. 26, Nr. 7/8, Bd. 27 u. Nr. 6, Bd. 28 dieser Zeit- 

 schrift, sowie in den zoologischen Jahrbüchern, Abt. f. Anatomie 



3 Müller, Fritz, 1861. Die Brachiopodenlarve von St. Catharina. 2. Beitrag. 

 Arcbiv f. Naturg. Jahrg. 27, Vol. 1. p. 55. 



39* 



