ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 227 



second, the thorax was present in the original Decapod stem. Some 

 work done by H. W. Conn, during the last summer, upon the larval 

 cuticle of crabs, indicates conclusively (it is claimed) that the latter 

 view is the correct one, or that at least Fritz Miiller's view is incorrect. 

 The larval skin, particularly the telson of a large number of crab 

 zoeas, was studied with the following results. 



The larval skin is not in different crabs alike, nor is it in any 

 case exactly similar to the inclosed zoea. There is always an in- 

 dication more or less complete, of some previously existing stage. 

 There has been shown in the various forms studied a gradation from 

 the larval skin, with little difference from the zoea inclosed, to a 

 larval skin which is utterly unlike the zoea, but which possesses a 

 forked tail with fourteen long feathered spines. This gradation is 

 complete, and a study of the different embryonic telsons shows that all 

 have been derived from the form shown by Panopeus, which has a 

 forked tail with fourteen spines. Now, such a larval skin is to be 

 considered simj)ly as the cast-off skin of some stage immediately 

 preceding the zoea. It has been shown by Paul Meyer that the study 

 of the skin of Macroura leads to a similar result, that a forked tail 

 with fourteen spines is also seen in the early history of this group. 

 If, therefore, a form can be found which shows these peculiarities, we 

 have reason for accepting it as the stem form of the higher Crustacea. 

 Now a study of the different protozoea forms which occur in the 

 ontogeny of various Macroura shows that we have in this form a stage 

 which fulfils the conditions. It has the forked tail with fourteen spines 

 and has large swimming antennae, another peculiar characteristic of the 

 crab larval cuticle. If the various larval skins of crabs and Macroura 

 be compared with each other, it will be seen that they are all to be 

 considered as modifications of a tail much like that present in the 

 larval skin of Panopeus ; and if this tail be compared with the 

 protozoea tail of Peneus, the likeness will be seen to be very striking. 

 We have, therefore, in the comparative study of the larval cuticle of 

 crabs, good reason for accepting as the stem form of the Decapods a 

 form which had resemblance to a protozoea. 



Gastric Mill of Decapods.* — F. Albert has studied the digestive 

 or gastric mill of Decapod Crustacea in great detail, in the descrip- 

 tions of which he makes use of the nomenclature proposed by 

 Nauck. 



The simplest arrangements of the hard parts in the gastric wall of 

 Decapoda are to be found in the prawn-like forms, where, however, 

 there is not so much a primitive type, as well-developed characteristics 

 which it is sometimes difficult to bring into association with the 

 majority of forms, owing to the absence of certain intermediate links. 

 Among the Natantia we find, on the one side, forms in which the 

 cardiac apparatus, and others in which the pyloric part of the organ 

 is best developed. In both cases the same plan has been followed ; 

 two paired and lateral teeth have entered into a physiological connec- 

 tion with an unpaired median process. At the end of one line of 



* Zeitschr. f. Wiss. Zool., xxxix. (1883) pp. 444-536 (3 pis.). 



