NO. 9 A NEW ORDER OF CRUSTACEA PENNAK AND ZINN 9 



From the standpoint of morphological characteristics and size (see 

 table i), it is logical to assume that larval stage 4, larval stage 5, and 

 the adult form a natural sequence. On the other hand, however, it 

 seems very probable that the three earlier stages are an incomplete 

 series and that there are still other early stages which were not dis- 

 covered during the present investigation. It is particularly likely 

 that there are very early larval stages which are comparable with 

 copepod nauplii in their simplicity. Because of incomplete informa- 

 tion concerning the various stages in the development of the Mysta- 

 cocarida, therefore, no attempt will be made at this time to assign any 

 descriptive, designative names to the five different types of larvae 

 that are known. 



Table i.—Suvunarizcd morphological characteristics of larval stages of 

 Derocheilocaris typicus 



5 o w o 



•" uafS 



1 3 



2 3 



3 3 



4 3 



5 3 



(adult) 2 



6S 



Internal anatomy. — Although only a superficial study was made 

 of the internal anatomy of Derocheilocaris typicus, it might be worth 

 while to indicate a few of the more obvious structural details. In 

 sexually mature individuals the most distinctive feature is a large, 

 elongate, dorsal, granular yolk gland; the posterior end of this yolk 

 gland extends as far as the fourth or fifth abdominal segment; 

 anteriorly, it may not extend beyond the first abdominal segment, or 

 it may extend as far forward as the second thoracic segment. The 

 ovary consists of several immature ova (customarily three to seven) ; 

 they are rather compactly arranged in the dorsal portion of the third 

 and fourth thoracic segments; often the ovary is partially imbedded 

 in the anterior portion of the yolk gland. A gonoduct could not be 

 definitely distinguished. The digestive tract is tubular and without any 

 pronounced constrictions or diverticula. Neither maxillary nor anten- 

 nary glands could be discerned. The nervous system, as shown by 

 longitudinal sections, is characterized by a series of extremely large 



