l54 AVERS. [Vol. VI. 



since they are without doubt descendants of the canal organs. 

 Fritsch has traced their development sufficiently to give us 

 assurance that they are transformed from the canal type during 

 ontogeny. 



Fritsch describes the processes of growth which determine 

 whether the canal line which, in the majority of Batoid forms, 

 occupies the place, and has the other anatomical relations, of 

 the line of Savi's vesicles in the Torpedinidae is to grow into 

 Savi's vesicles or to remain a canal line. He says, "Verschmel- 

 zen die dunnwandigen,aberfesten bindegewebigen Haute, welche 

 den Lymphraum begrenzen, da miteinander, wo sie zwischen 

 den Sinneshiigeln an einander stossen, in vorwiegend sagittaler 

 Richtung, so werden Canale daraus, Verschmelzen sie allzeitig 

 an den Grenzen der Ausbuchtungen fiir die Sinneshiigel, so 

 werden aus diesen SAVi'sche Blasen." 



As to the identity of position in the two groups of Batoids, 

 he observes, " Wie die Reihen der SAVi'schen Blasen von der 

 Ventralseite vorn an der Schnauzenkante zur Dorsalseite treten, 

 so treten an gleicher Stelle die ventralen Kopfcanale der ge- 

 meinen Rochen in die Ruckencanale iiber." Our author men- 

 tions transitional stages between the open canal and the closed 

 vesicular organs, and after stating that in histological charac- 

 ters the two sets of organs likewise agree, concludes that " Aus 

 alien diesen Vergleichungen ergiebt sich, dass die SAVi'schen 

 Blaschen abgerundete und ganzlich abgeschlossene Stiicke 

 haiitiger Kopfcanale anderer Rochen darstellen," and that 

 we need no longer be surprised that the Torpedoes possess a 

 system of organs which is lacking in all other Batoids, but 

 which is represented in these forms by the more primitive canal 

 type. 



The special interest which Savi's vesicles have for us at this 

 time is due to the fact that they constitute a second closed sys- 

 tem of organs derived from the wide-spread, open canal type, 

 and which in this respect have advanced along the same line of 

 differentiation as the auditory organs, and must be subject to 

 the same conditions as the ear hairs in the reception of sound 

 waves, he adds (p. 133): "Die unter verschiedenen Namen, wie 

 Seitenkanalsystem, SAVi'sche Blaschen, und LoRENZiNi'sche 

 Ampullen, bezeichneten Canale unter der Haut der Torpedineen 

 stellen verschiedene Glieder eines in der Uranlage einheitlichen 



