Other Pelagic Arthropoda. 

 Period IV — August 1-4. 



475 



Depths. 



Average. 



Day. 



Night. 



Meters. 



No. 



Per cent. 



No. 



Per cent. 



No. 



Per cent. 



0—3 







0.0 







0.0 







0.0 



3—6 







0.0 







0.0 







0.0 



6—9 



5 

 13 



27.8 

 72.2 



7 

 8 



46.7 

 53.3 



3 



18 



14.3- 



9—12.. 



85.7 



12—15 







0.0 







0.0 







0.0 



15-18 







0.0 







0.0 







0.0 



Total . 



18 









21 















OTHER PELAGIC ARTHROPODA. 



Four animals, other than those already described, were ob- 

 tained in considerable numbers during our observations, al- 

 though they were not numerous enough nor present with 

 sufficient regularity to give any clear conclusions as to their 

 vertical distribution. The first of these is Diaphanosoma brachy- 

 urum Fisch. Scattering individuals of this species were ob- 

 tained in Period I, the total number being 16, with an average 

 of less than 2 for each series of observations. In Period II r 

 109 were taken, giving an average of about 4 to an observa- 

 tion. In Period III, 276, or an average of nearly 20; and in 

 Period IV, 1135 were obtained, giving an average of nearly 10Q 

 for each set of observations. It is obvious that we have during 

 July the beginning of the story of the development of Diaphan- 

 osoma, and observations made later in the year confirm this 

 idea. In August three observations showed a catch of 400 to 

 600, and in September the number of Diaphanosoma rose to a- 

 maximum of more than 1000 per series of observations, and the 

 species disappeared in October. The vertical distribution of 

 this species follows very closely that of Cyclops and Diaptomus. 



Leptodora hyalina Lillj. was constantly present in our collec- 

 tions, but in very varying numbers. As stated in the account of 

 our methods, all of the individuals belonging to this species were 

 counted, and from all of the observations a total of 347 individ- 

 uals was obtained. This would be an average of about 6 speci- 



