irite i. 



Constitution 



, Uniannulate. 



ii. 



}> 



Triannulate. 



., iii- 



)J 



Triannulate. 



„ iv. 



>> 



Triannulate. 



v - 



5> 



Pentannulate. 



BY E. J, GODDARD. 857 



The first unabbreviated segment is v. The following table 

 shows the constitution of the abbreviated segments anterior to v. 



Annuli 1. 

 ,, 2,3,4. 

 „ 5,6,7. 

 „ 8, 9, 10. 

 „ 11,12,13,14,15. 



At the posterior extremity of the body we find somites xxiv.- 

 xxvi. abbreviated. 



In Dina and Herpobdella, the two forms to which this leech 

 bears the closest resemblance, we find that the abbreviated 

 somites include i.-v., and i.-iv.. respectively, at the anterior 

 extremity; xxiv.-xxvi , and xxiii.-xxvi., respectively at the 

 posterior extremity. 



On close examination of the anterior portion of the body 

 under magnification, it is noticed that the annuli are not exactly 

 alike. The last annulus of each somite is slightly more important 

 in size than the third and fourth, but much more so than the 

 first two annuli. The first two are equal, and the third and 

 fourth are of equal importance. 



The diagnosis of Dina given by Blanchard is : — " Somitus e 5 

 annulis constans, tertio majore et transverso diviso. Oculi et 

 clitellum ut in Herpobdella. Soiniti i.-v., et xxiv.-xxvi. contracti." 



I take it as granted that Blanchard adopted Whitman's method 

 of determining the somites, since Castle's paper has been published 

 much more recently. 



If this is the case then the annulus which would be the third 

 according to Whitman would be the last annulus of the somite 

 according to Castle; and it is the corresponding annulus of the 

 somite in the present form which is strongly developed. The 

 anterior four annuli of the somite, however, are of equal import- 

 ance among themselves in Dina, whereas they fall into two 

 consecutive sets in the present form. This differentiation of the 

 annuli composing a somite is not so well marked towards the 

 posterior extremity as towards the anterior end. 



