392 PROCEEDINGS OF THE ACADEMY OF [1893. 



more slender, sharp pointed and spine- like. At the same time 2 or 

 3, or even 4 smaller cusps are formed on the outer side, and one (an 

 endodont) or sometimes two cusps on the inner, so that there are 

 typically 4 or 5, sometimes 6 or even 7 cusps on a tooth (see fig. VI 

 first lateral in the second and fifth transverse rows. ) This peculiar 

 formation of the inner group of laterals is found in the embryonal or 

 larval stage of the animal only ; and in order to have an appropriate 

 name for this form of tooth, we may properly term it echinate. 



The teeth, passing through the echinate stage, gradually again 

 change in form ; the body of the tooth becomes longer, the mesodont 

 loses its spine-like form, becoming wider, and its free cutting point 

 shorter ; the endodont becomes more coalescent with the mesodont, 

 with a short and less acute point ; but it remains constant, being 

 visible in all specimens in different stages of growth which were 

 examined, from this locality. 6 



Further modifications are that one or two of the distal cusps dis- 

 appear, and the one or two remaining are transformed into the single 

 ectodont of the adult (conf. fig. VI, the first lateral in the eighth to 

 eleventh transverse rows); moreover the plate of attachment begins 

 to be prolonged backward, at first being very thin and small, barely 

 visible. The outcome of this series of changes is the perfect lateral 

 tooth of the adult Limax. 



All of the forms above described may be seen in one transverse 

 row, (as represented in the fifteenth row of fig. I), and the different 

 stages of transformation are shown in every longitudinal row of the 

 same figure and fig. VI ; but it must be added that the transverse 

 rows, especially in the anterior part of the radula, are closer together 

 than represented in the drawing, in which they are separated for the 

 sake of distinctness ; and the cusps reach further backward over the 

 body of each following tooth. The individual teeth are fully as wide 

 in the front part of the radula as more posteriorly. 



(2). The distal laterals are evolved through other intermediate 

 stages much resembling those undergone by the later aculeate mar- 

 ginals, as illustrated in figs. II- V. Fig. II represents at A the 

 thirtieth, at B the forty- fifth transverse row of teeth from a spec- 



6 It may be noted here that in the persistence of the endodont, Limax cam- 

 pest ris offers no distinctive character from Limax agrestis Linn.; and it may be 

 added that in drawings made in 1882, of the radula of Limax tenellus Nils, 

 and L. cinercus Lister, from the Swiss Alps, the endodont is distinctly shown. 



