18 Mr. H. J. Carter on Freshwater Rhizopoda 



The last two or three normal segments in Insects (that is, the 

 16th, 17th, and 18th) are frequently wanting. 



In the above homological comparisons it is assumed that the 

 three anterior normal segments present in a Crustacean are 

 normally and potentially present in an Insect. This will be con- 

 sidered by many as the doubtful point in the above comparisons. 

 But it is proved to be correct by the fact that these three seg- 

 ments are sense-bearing segments in Crustaceans, and the Insect 

 fails in no sense belonging to the Crab. As stated on page 188 

 (Annals, /. c), the absence of a jointed oi-gan is no proof of the 

 absence of the segments, unless it be true also that the corre- 

 sponding sense is wanting. 



If the constitution of the anterior part of the head in the 

 Insect be still questioned, there is nevertheless good reason for 

 making the mandibular segment in the Articulate type (as it ad- 

 joins the centre in embryonic development, from which progress 

 goes on forward and backward) normally identical in all groups 

 under that type ; and hence from this segment, or No. 4 in the 

 Crustacean series, on to No. 18, the parallelism between the 

 Insect and Crustacean must be rightly given ; consequently, if 

 there is any doubt, it holds only with regard to Nos. 1, 3, and 3. 

 The law of unity of structure under a type seems, however, to 

 preclude even this chance for doubt. 



Comparing the higher Decapods among Crustaceans and the 

 higher Insects, the mean size or mass is about as 50 to 1. This 

 ratio indicates approximately the amount of condensation in the 

 Articulate structure connected with the elevation of grade from 

 the typical Crustacean to the typical Insectean. 



III. — On Freshwater Rhizopoda of England and India; with 

 Illustrations. By H. J. Carter, P.R.S. &c. 



[Plates I. & II.] 



The object of this communication is to bring together descrip- 

 tions and illustrations of the freshwater Rhizopoda which I have 

 found in England since my return from India in 1862, and also 

 to add some of those which from time to time came under my 

 notice in the island of Bombay, in order that I may, to a certain 

 extent, show what species are common to both localities, and 

 also some of those which may be peculiar to Bombay, or at least 

 may not yet have been described. 



Further, I have drawn most of these on the same scale, and 

 have added some of their varieties respectively, so that an idea 

 may be thus gained of their sizes generally, as well as of some 

 of their differences in point of shape ; for, unless they are treated 



