260 EMBRYOLOGY 



is said to be the case in the Trochophore. In the Rotatoria 

 there are two trunks to the excretory system, which in the 

 Gastrotricha, which are related to the Rotatoria, open to the 

 exterior by means of two ventral openings (Zelinka, No. 

 12), so that this organ thus acquires still greater resem- 

 blance to the so-called head kidney, the excretory system of 

 the Trochophore, for the two head kidneys also open directly 

 and separately from each other to the exterior (comp. p. 266) 

 The agreement of the Rotatoria with the Trochophore was 

 especially advocated by Hatschek (No. 1), with whom 

 recent investigators of the Rotatoria, such as Plate and 

 Zelinka, in the main agree (Nos. 3, 4, 11, 12). 



Tessin contends against the relationship of the Eotatoria to the An- 

 nelida or their ancestral form, which we have briefly indicated above, 

 because, owing to the origin of the trochal organ from the stomodeal 

 invagination and the position of the brain outside of the area included 

 within the trochal organ, a comparison of the trochal organ with the 

 ciliated rings of the Trochophore larva does not seem to him admissible. 

 Tessin seeks rather relationships to the Turbellaria, being influenced by 

 the lobular structures of the embryo. His comparison of the caudal 

 appendage of the Eotatoria with the post-abdomen of the Crustacea, 

 which he supports with the fact that a process of the entoderm is said to 

 extend into the tail, seems weak. This perhaps indicates that the 

 Eotatoria have a tendency to increase in length. We would here recall 

 the growing out of the Trochophore into the worm. Eelationships of 

 the Eotatoria to the Arthropoda have also been found in forms such as 

 Hexarthra polyptera, to which attention has recently been called by Plate 

 (No. 4). This remarkable Eotifer, discovered by Schmaeda, possesses on 

 the ventral side three pairs of movable setose appendages, which are like 

 extremities, and give to it almost the appearance of a Nauplius. In view 

 of the close relationships of the Eotatoria to the Trochophore, one will 

 certainly not think of a descent of the Eotatoria from the Arthropoda, 

 especially from the Crustacea; it is, however, interesting to see how 

 Trochophore-like beings can vary in the direction of the Arthropod type, 

 even if it be only in their outward shape. 



Still less justifiable than a comparison of the caudal appendage (foot) 

 of the Eotatoria with the abdomen of the Crustacea is such a comparison 

 with the foot of the Mollusca, which has been attempted by various 

 writers, who have based their conclusions principally upon the position 

 of both organs between the mouth and anus, which is particularly well 

 expressed in embryos and larvte. 



