528 MAYNARD M. METCALF, 



The Diplosomidae. 



Of this family also I have but a single representative species — 

 Diplosoma listerianum Della Valle (Plate 37, Fig. 51). 



This species has a small gland whose ventral wall is composed 

 of lightly staining cells Hke the vesicular cells of Amaroecium, Its 

 rapheal nerve is evident. It has but few ganglion cells. 



I have not studied the Coelocormidae or Polystyelidae. 



The compound Ascidians in general, and Comparisons 

 of the compound and simple Ascidians. 



It must be evident to one who has read thus far, that, so far as 

 the character of the neural gland is concerned, the compound As- 

 cidians fall into two natural groups. In the first group are the 

 BotryUidae, with the gland dorsal to the ganglion and divided into 

 two portions, an anterior spindle-shaped chamber filled with disinte- 

 grating cells, and a posterior solid portion fused with the ganglion. 

 In one genus of this group, Polycydus, the solid portion of the gland 

 contains peculiar cells with paranuclear bodies. In the second group 

 of compound Ascidians, consisting of the Disiomidae, Polyclinidae, 

 Didemnidae and Diplosomidae, the gland is ventral to the ganglion 

 and shows no division into two parts. The gland of these forms, as 

 indicated by the histological character of its cells, evidently corresponds 

 to the posterior part of the gland of Polycydus. The anterior chamber 

 of the gland in the Botryllidae is not present in the species of the 

 second group. Of course it is represented by the unmodified portion 

 of the duct next to the ciliated funnel. 



The histological difference between the two portions of the gland 

 in Polyeydus suggests a difference in function. As the function of 

 the neural gland is wholly unknown, it seems hardly worth while to 

 discuss this further. 



The cells of the gland of the second group of compound Ascidians, 

 as I have divided them, show an interesting variety of histological 

 conditions. In Fnigaroides, Amaroecium and Diplosoma we have found 

 vesicular gland cells containing a single vacuole. In Circinalium either 

 idle vacuole has a central coagulum, or else the cells are unvacuolated, 

 and contain from one to three lightly staining paranuclear bodies. The 

 gland of Frayaroides in addition to its clear vesicular cells may have 

 also cells with one to seven similar paranuclear bodies. In Polycydus, 

 one of the other group of compound Ascidians, I have found para- 

 nuclear bodies in the gland cells, and, among the simple Ascidians, 



