558 SUMMARY OF CURRENT RESEARCHES RELATING TO 



away tbo ripe elements that Lave been formed in it. Tlio gland is 

 merely a connective reticulum in which nuclei are scattered. 



In Mollusca the lymphatic gland is generally placed near the 

 respiratory ajiparatus ; in Gastropods it varies considerably in position 

 and relation. 



In the Oligochreta the amcebocytes are formed by the so-called 

 hepatic layers of the intestine ; in Hirudinea they form the bothryoidal 

 tissue of Eay Lankester ; the cells are often of large size, and contain 

 large yellow or greenish granules. The blood of Gephyreans has a re- 

 markable likeness to that of lower Vertebrates, well marked amcebocytes 

 with a yellow ferment and nucleated corpuscles containing a colourless 

 liquid different from hasmoglobin being found in it ; in the Tunicata 

 there appear to be two kinds of elements, but they are very different 

 from those of Vertebrates. 



Pelagic Animals at Great Depths and their Relations to the 

 Surface Fauna.* — Dr. C. Chun has made a number of iuteresting and 

 important observations on pelagic animals living at great depths, which 

 are reviewed by Prof. Alexander Agassiz.f From a depth of 1300 metres 

 Dr. Chun brought up a large pelagic fauna ; small crasj^jcdote Medusje, 

 Ctenophores, Tomopteridte, Sagittee, Alciopidse, larvae of Decapod Crus- 

 tacea, Ajypendicularise, Pteropoda, and small transparent Cephalopods. 

 Dr. Chun assumes that there were no currents at the spots whence ho 

 obtained his rich hauls, but Prof. Agassiz thinks there is nothing to 

 show that when so near the shore as he was there is not a more or less 

 active interchange of the fauna from the shore slopes to that of greater 

 depths. If a deep-sea pelagic fauna should be found in the deep water 

 of oceanic basins it would help to explain the manner in which the deep- 

 sea fauna obtains its food. Prof. Agassiz thinks that Chun's results 

 merely prove that in a close sea (the Mediterranean) near shore there is, 

 even at considerable depths, a great mixture of true deep-sea types and 

 surface pelagic animals which sink at certain times far beyond the limits 

 usually assigned to them. 



Many of the so-called surface pelagic types have been proved by 

 deep-sea expeditions to be the young of abyssal species. Chun has, 

 however, clearly proved that many embryonic stages of surface pelagic 

 animals are only found at considerable depths. Deep-sea fishing with a 

 properly closing net promises to be a material help to embryological 

 investigations. 



Dr. Chun considers that the great increase of temperature at the 

 surface compels surface pelagic animals to seek cooler depths ; while 

 allowing this for some groups. Prof. Agassiz thinks that the calm or 

 ruffled condition of the surface is a more powerful influence. It is only 

 on calm nights that a good harvest of surface animals can be obtained. 

 In his own experience of surface collecting Prof. Agassiz " never met 

 w4th such prodigious masses of surface pelagic animals as on the hottest 

 days of our dredging expeditions. When the sea happened to be smooth 

 as glass under a blazing tropical sun it seemed as if the water was nearly 

 solid as far as the eye could reach with countless surface animals of all 

 sorts." 



Prof. Agassiz thinks that there is nothing to show that the more 

 active deep-sea Crustacea, Fishes, Cephalopods, Pteropods, Annelids, 



• Bibliotheca Zoologica, i. (4to, Cassel, 1888) pp. 1-G6 (5 pis.), 

 t Amer. Joura. Sci., xxxv. (1888) pp. 420-4. 



