328 Mr. H. J. Carter on the 



Entering, now,upon the chief subject of this communication, 

 it will, for convenience, be desirable to divide the development 

 of the living sponge-ovule into four periods, viz. : — 



1. That from its earliest appearance to the commence- 

 ment of the duplicative division of the yelk. 



2. That from the first duplicative division of the yelk to its 

 ultimate duplicative subdivision. 



3. That from the formation of the embryo to its fixation or 

 stationary position. 



4. That from the stationary position of the embryo to the 

 development of the perfect sponge. 



FiEST AND Second Periods. 



As the first and second periods are taken from Halisarca 

 lohularis, it is desirable to premise a description of the ovi- 

 parous state of this sponge in both these periods ; but as the 

 former has already been done (' Annals,' 1874, vol. xiii. p. 433), 

 there is no occasion for a repetition of it here, though it is 

 necessary to add to my former description that the surface of 

 Halisarca lohularis is covered with vibratile cilia (PL XX. fig. 1, 

 ee), which is not the case with that of Halisarca Dujardinii. 



In the second period, however, it differs in that the ova are 

 greatly enlarged, and, instead of being diffused throughout 

 the substance of the sponge, are gathered, as before stated, into 

 heaps at its base (fig. 1, hh)^ where they rest upon the bare 

 rock on which the sponge has grown (fig. 1, cc). 



Here, too, although they are respectively encapsuled, the 

 heaps or groups are each as respectively enclosed in a common 

 membrane (fig. 1,^), which appears to be a dilated form of 

 the excretory canals opening at the vent (fig. 1,/"), by which 

 the embryo (fig. 1, i) when it leaves the capsule (fig. 1, k) 

 can find an easy exit. Further, the parent sponge has be- 

 come reduced to a mere shell or layer (fig. 1, aa)^ in which 

 however, the spongozoa of the ampullaceous sacs, as before 

 stated, seem to present a more intensified red or pink-violet 

 colour than ever (fig. 1, <?), and the vents show themselves to 

 be provided with a sphinctral diaphragm of sarcode (fig. 1,/") 

 somewhat conti-acted, as if to regulate the egress of tlie em- 

 bryos. 



First Period. 



That from the earliest appearance of the ovum to the com- 

 mencement of the duplicative division of the yelk. 

 If we take a portion of Halisarca lohularis, at any time of 

 the year probably (if it is not too young), and tear it to pieces 



I 



