186 NOTES AND MEMORANDA. 



phenomena of amoeboid movement. The mesoderm tissue is 

 a true connective tissue. There are in the cortical region of 

 the sponge regular systems of branched inhalent and exha- 

 lent canals, the main stems of which run almost parallel to 

 one another and at right angles to the outer surface of the 

 sponge mass. The branches of the canals are thickly beset 

 with ciliated chambers^and it is through these chambers,many 

 of which have two canal branches opening into them for the 

 purpose, that the inhalent and exhalent canal systems com- 

 municate with one another. One instance was observed in 

 which four canals opened into a single ciliated chamber. 



The cortical portion of the sponge is distinguished from 

 a deeper region where there are no ciliated chambers present, 

 but where the generative elements are developed in the meso- 

 derm. 



The Halisarcas and also a number of other sponges exa- 

 mined by Schulze, viz. amongst siliceous sponges Reniera 

 informis, Spongilla lacustris and ^S*. Jluviatilis, and amongst 

 horny sponges Aplysina aerophoba, in all of which this 

 observer has clearly made out and investigated the sperma- 

 tozoa are dia3cious. All former observers, as e.g. Eimer and 

 Haeckel, have found in the species examined by them sper- 

 matozoa and ova in the same sponge. Both male and female 

 elements are developed out of rounded cells with dark granu- 

 lated contents occurring in the mesoderm, but the origin of 

 which was not determined. Both elements become developed 

 in cavities formed in the mesoderm tissue, which are clad with 

 a layer of polygonal endothelium cells. The spermatozoa 

 have an elongate, egg-shaped head, a smaller front part of 

 which, is marked off from the hinder larger part by a con- 

 striction. The tail of the spermatozoon, which is 0'08 mm. 

 in length, is set on to the head on its side and not at either 

 of the ends. Out of the one rounded cell a large mass of sper- 

 matozoa are developed, and out of a similar single cell only 

 one ovum. Hence, as in many other animals, the single egg is 

 equivalent to a mass of spermatozoa. 



The segmentation of the ovum is, as was determined by 

 Carter and Barrois, a complete one, but sometimes irregular. 

 The segmentation cavity is first to be observed when sixteen 

 cells have been formed. It was found impossible to keep the 

 larva, which is equally ciliated all over at the time of its 

 emergence, alive long enough to observe its further develop- 

 ment. Schulze was no more able than Barrois has been to 

 observe an invagination or formation of a gastrula. 



The above remarks refer to the structure of Halisarca 

 lobularis. In H. Dujardini the ectoderm both on the outer 



