TYPE OF THE INTESTINELESS CHILOSTOMATOUS LARVA. 25 



has been described in detail by Barrois (No. 9). Here also we 

 find the oral and aboral surfaces separated by a corona of somewhat 

 large ciliated cells. The aboral surface shows the well developed 

 retractile disc surrounded by a circular mantle-cavity ; on the oral 

 surface, the ectodermal furrow with its ciliated tuft and the sucker- 

 invagination are situated. Strong pigmentation is often found in 

 the larvae of this and the following types, paired patches of pigment, 

 like eye-spots, being found in individual cases. The most essential 

 distinction between the larvae of this type and the Alcyonidium 

 larva is the entire absence of the alimentary canal. We assume 

 that the inside of this larva contains only the so-called central tissue. 

 In the very imperfect state of our knowledge of the anatomy of 

 these larvae, it must still be regarded possible that many of them 

 may possess a well-developed alimentary canal. We are therefore 

 unable at present to define exactly the distinctions between this 

 type and the one last described. 



The metamorphosis of the larvae of this type will be described 

 together with that of the following type. 



3. Type of the intestineless Chilostomatous Larva with 

 highly-developed corona. 



a. Structure of the Larva. 



We shall take as type of this group the larva of one of the 

 Cellularhia, the Bugula larva (Fig. 9), which has become well known 

 to us through the researches of Nitsche (No. 22), Claparede (No. 

 10), Salensky (No. 37), Barrois (No. 9), and Vigelius (Nos. 39 

 and 40). The intestinal canal here also is altogether wanting. The 

 primary entoderm changes direct into the so-called central tissue 

 (Fig. 9 B, f). The distribution of the ectodermal organs is the 

 same as in the larvae of the Alcyonidium and the EscJiarina types; 

 the whole form of the larva, however, is somewhat different, 

 chiefly on account of the great growth of the coronal cells (c) in 

 the direction of the principal axis. These cells lengthen greatly, the 

 whole of their surface becoming covered with cilia, while in the 

 larvae of the preceding types these cells usually bear only one row 

 of cilia. This extension of the corona encroaches greatly on the 

 aboral and oral surfaces. The retractile disc (r) is consequently 

 smaller, and the ectodermal furrow (e) is so grown over by the 

 increasing coronal cells that it at last appears enclosed by the coronal 

 region. In this way a more or less spherical or rounded larva is 



